Skip Florence for Siena?

NO, NO, NO

Skipping Florence and staying in Siena probably runs against the 'conventional wisdom', but given what your expressed interests are ( and are not), doing as you suggest is OK.

You can do Florence on another trip; it is not going away.

I do have to tell you about my sister-in-law's experience. They went to Florence a few years ago and, like you, they aren't museum goers so they skipped the Uffizi and David. (Insert my scream here!) They did go into a few churches, but mostly wandered around. But here's the kicker: They absolutely loved it.

If you have the Rick Steves Italy book, I encourage you to read about both cities, and then decide for yourself.

Do not skip seeing David! It doesn’t take long.
Tasty in Florence, take a day trip to Siena.
You only have 9 nights in Italy? I guarantee that you’ll return!

I am unclear as to where is your cooking class is located and where your wine tour starts. This would help determine your decision. Based on what your interests are, architecture, churches and history I would suggest Florence. It fits all three. Siena is interesting and enjoyable, but IMO 2 days is plenty. So if you choose Siena, I would consider adding a night in Rome. Enjoy Italy!

Some places in Florence are seminal in architecture history: the Duomo dome, the facade of S.Maria Novella, porticos in piazza SS. Annunziata. However, the urban landscape in Siena is more interesting due to hills, so you may skip Florence if you prefer.

This could be a good time to go. I would not substitute Siena for Florence. The duomo sights in Florence are pretty great. Florence would probably give you more to do indoors during what could be a rainy time. Cathedral in Siena is quite nice too. You might need a break from the larger cities though, I did an all-urban trip to Italy this year and it was exhausting. Siena can be crowded too but this time of year might be a welcome respite. Venice is not a “big” city but it punches above its weight in the impact of crowds. Orvieto is also worth considering for a break in the middle.

Tough call especially since you like history, churches and architecture. Lots to see without even going to a museum. I love both Siena and Florence. Siena seems to have more of a small town feel IMHO.
This is your trip and you should plan accordingly. I would do your homework and watch the RS travel videos and maybe try to get another perspective by watching Smart Travels or Samantha Brown’s episode on Florence or Siena. I made a similar decision a few years ago and left off Granada from my Andalusian itinerary. It allowed me to hike and explore some of the small towns which is exactly what I wanted.

Thank you for the responses. I am reading a few of Rick Steves' travel books, so that should help our decision. I am positive we will be happy with either choice, but we are leaning towards Florence. Florence would save us some travel time as well. Thanks!

Florence is not one of my favorite places in Italy, not by a long shot...and if you visit the museums you can practically kill yourself with Renaissance overload...it's just too much... And yes, David is special but how many separated heads can anyone look at in one crowded museum?? Hundreds if you go. But, that said, there are many things to see and do there so I would give it a day or two.
Sienna has always been one of my favorite places....but it has certainly managed to attract larger crowds in recent years. It's still worth going and by staying there you can enjoy the early morning and late afternoon when things slow to a more local pace.
Most folks stay in Florence and day trip to Siena. With your interests you might be someone that should consider staying in Siena and daytripping to Florence...
If you can, add night or two (or more) to Rome.

You are going in a great time of the year. Crowds should be smaller. It's a tossup between Siena and Florence. There's plenty to do in either town other than museums.

I suggest you sit down and work on a detailed itinerary, including travel times between cities. This will give you a more realistic idea of how much time on the ground you have. Include arrival times and departure times for flights. Since you've booked, you'll know when you arrive and when you leave. Try not to cram in too much.

Prepare to fall in love!

I am thinking I'll be overloaded with Renaissance art in Florence - I'm not thinking about skipping Florence, but lately I have been thinking about drastically reducing my time there to spend more time in Siena. I had thought I'd do a day trip there from Florence, but now I'm kind of wishing I'd planned it the other way.

I don't know what you should do, but I share your questions. I'm going to be in Florence 5 full days/2 half days in October; I've paid for my Florence apartment, but I still might take an overnight in Siena anyway.

Given your interests (or lack thereof with regard to art), I think it is perfectly fine to go to Siena instead of Florence. If you regret it later, you will hopefully be returning to Italy anyway. Some people absolutely love Florence. In my case, while the art is unparalleled in my opinion, I did not fall in love with the city itself. It was actually my least favorite place on my first trip. But I wouldn't have missed the art for anything. Siena is wonderful in its own right. Do what you think will make you happy! Buon viaggio.

Both are wonderful. Since you are going for the first time, I can't imagine skipping Florence. The Duomo is a sight to see for sure. However, so is Siena. Personally, I would not need to spend 3 days in Siena though. Florence would be more exciting. It just depends on what you have a feel for!

In addition to reading, try watching videos, including Rick's, which are here under "Italy": https://www.ricksteves.com/watch-read-listen/video/tv-show

The two cities are very different in every way, from size to feel to history. So, see whichever one or ones calls to your more at this time. There is no right or wrong answer, and you can't do it all on one trip, so don't worry about what you'll "miss" - you'll be seeing something else in exchange.

Go to Florence and, if you have the time, take a day trip to Siena.
Your trip is too short, and the logistics of settling in Siena, day trooping to Florence, and then going to Rome, will waste additional time.

I would not skip Florence. It's a must to see and frankly 3 days isn't excessive. Taking into account travel time from Venice and to Rome, you'll be rushed if you choose to stay in Siena. There is no direct train connection from Siena to Rome, I believe. And if you choose to have a day trip to Florence from Siena, you'll be short on time to add anything else to Uffizi that requires reservation and/or standing in line for admission. We went to Florence twice, and only on our second visit we felt like we saw enough of Florence to add a day trip to Siena. Siena is beautiful but can easily be done in one day whereas Florence can't. But like I said, the train connection to Rome would be a deciding factor for me. You'll have to change trains if you go to Rome from Siena. From Florence it's an easy direct fast train, and plenty of them too. Not just Trenitalia but Italo too (private).

Both are marvellous cities. My personal choice would be Siena over Florence, but Siena is probably my favourite city anywhere.
For the OP, Florence makes far more sense for the logistical reasons stated.

I definitely think it is a personal decision based on personal tastes. I enjoy art, but have to say that I have been underwhelmed by Florence both times that I have been there. I wanted to like it since everyone seems to rave about it but it is just okay and now that I have been twice, I am in no hurry to return. This last time was so crowded that you could not get anywhere near the ponte vecchio and the courtyard near the Uffizi was insane.

Siena, on the other hand, I loved for the small town feel while still having beautiful architecture and some notable art. We were far more comfortable in the hill towns of Tuscany than the larger city of Florence with all the people and tourists.

So decide if you like being in large crowds and jostling with other tourists or if you want to relax in a small town and enjoy beautiful scenery and architecture.

Given that you won't even be in the town for very long, Siena should have plenty to keep you busy. I don't know what the weather is like then, but grabbing some food and enjoying it in the Campo is a great way to hang out. I don't remember anything like that in Florence. You could always go up to Florence for part of a day to see the Duomo (buy tickets ahead of time if you're going to climb) if you feel like you'd miss out otherwise. Siena would be a little more laid back than Florence, if you wanted to relax a bit in between a couple of busier cities.