Why is Valencia not mentioned in Rick Steves book at all? skip?

Rick Steves guide books aren't meant to cover every corner of every country. He has chosen what he considers the highlights--others disagree, and that's fine.

I'm about to go to Valencia for the 2nd time. As the first time, I'm meeting a group of friends, one of whom lives in Valencia, for the Las Fallas festival. If not for that, and the Paella that is a speciality of Valencia, I might not think it was worth more than a day. That doesn't mean there is anything wrong with Valencia--it's probably a great place to live, but it doesn't have many of the things that a tourist would find worth visiting.

The RS guides skip a lot of places that I have really enjoyed. They cover the places that are popular with Americans. RS travel guides are excellent, but don't plan your trip with just one guide book. I like to use Lonely Planet and Let's Go books for their different perspectives.

With that said, you will have your hands full seeing Madrid, Barcelona, and Seville in just 11 days.

For the same reason that he ignores Zaragoza.
These 2 cities are the 3rd and 4th largest in España.

We loved our 3 days in Zaragoza.
Ate the single best pintxo of my life there at El Méli del Tubo.
Went to a great museum - EMOZ.

Rick's guidebooks have always been selective, not like the competitor books, for about the last 4 decades at least.
It doesn't mean you can't go there.

I also recommend Rough Guides and Michelin Green Guides.

I second the Rough Guides recommendation.

I prefer them to Lonely Planet, which often feel encyclopedic and hipster to me.

I jus bought a Rough Guide for Poland and it’s probably the guidebook that’s most similar to Rick Steves, except they cover every region of the country and offer info about lesser-known destinations.

I spent a couple nights in both Valencia and Zaragoza this past year, enjoyed them both. But I would list Cordoba and its Mesquita ahead of both if choosing among them. The Mesquita is very special, with a Catholic Cathedral built inside an ancient, beautiful and unique mosque. Lots of other places to visit in Cordoba too, plus, it has the advantage of being on the AVE train route between Madrid and Seville. If you can arrange to fly into Barcelona and out of Sevilla, or vice versa, that would be ideal, and reduce your time in transit in Spain.

RS recommends the "must see" sites in Spain, but if you have time I would recommend Valencia. The old town is lovely and the City of Arts & Sciences it amazingly odd and beautiful.

There are lots of great cities to visit in Spain. Unless you want to spend a couple of days looking at European paintings at the top-notch art museums, Madrid would not make my top 15 must-sees in Spain. How many nights do you have on the ground? You have 11 days only if you have 12 nights. With only 10-11 nights, going to more than 3 cities is too much. My top 3 would be Barcelona, Granada (for the Alhambra) and Sevilla.

As for the RS guides, the ones I've used seem to be concentrated on the places his tours go to. For instance, I have the RS France guide from 2 years ago and in 1149 pages, I found Marseille mentioned once in the text, as an aside. It's as if the second largest city, with a history going back to its founding by the Greeks, had been a major seaport since then. He has over 200 pages on Provence and the French Riviera, describing many towns and villages within a couple hours drive from Marseille.

OTOH, since his tours go to Madrid, Barcelona and Sevilla - and Granada - they are all in the RS book.

Definitely spend some time in Valencia. Friendly people, great food and an awesome market. Like others have said, RS books are great for the areas that are covered, but many wonderful destinations are not included. I also use Lonely Planet and Fodors