clothes for early October

Do you mean a Rick Steves tour to Spain?

I'd say no. Tours are pretty casual. You sightsee all day and then often head to dinner from your last activity on the nights where there is a group meal. I have not been on a tour in Spain but that has been the case for the other 11 tours I've done, lol.

Rick Steves tours have always been pretty casual, and I've not found Spain to be particularly dressy in general.

We were in Spain in November a few years ago and didn’t feel like people were “dressy”. People used to recommend dressing up in Europe to avoid looking like a tourist (and therefore being less of a target for pickpockets). Europeans (including the pickpockets) will still know you’re a tourist regardless of what you wear, so wear what is comfortable for you.

The dressiest I ever have are Dockers and polo type shirts. My wife has nice slacks and tops/sweaters. I guess it depends on what you plan on doing and where you’re going. In years past when people were out for the evening stroll, many or most the older generations wore nicer clothes. That’s not necessarily the case any longer. Wear what is comfortable to you, yet somewhat conservative if going into a church, e.g., no short shorts or mini skirts for females and no sleeveless shirts.

It would be nice to know why your friends said what they said, i.e., were they referring to some specific event or situation.

... uhmmm that'll depend on what you plan to do during your visit, right?

I always pack something nice for my audience with Enric in Barcelona.

How many bags are you taking? Me, I go carryon-only so I usually have a travel blazer with me. It is from Eddie Bauer, a lightweight and formless, but dressy, garment that gives me a veneer of presentability. Something similar is certainly available for women. The dressiness required at any destination is easily researched ahead of time.