Hello fello travellers, my husband and I would like to go to Spain this fall, it would be our first time there. We're in our mid 40s, we love pretty much everything, foodies at heart, catch diffenent sites, and enjoy just walking the streets of a great city! We don't want it too rushed, so this is why I only picked 3 base cities. I'm thinking about 4 days in each would be fine (with day trips in between). Here are my quesitons: What are the must see day trips? What's the best way of getting from one base to the next, plane or train? Any smart order to do them in? Lastly, what are some good not too expensive hotels to stay at? Any info would be great. Thanks to all.

So you already picked your three 'base' cities? I'm sure that at least one of them would differ from mine. But first things first:
What is the planned duration of your trip: 2-weeks?
Arrival and departure airport(s)?
Your three proposed 'base' cities?

Peens,

The "must see day trips" would be determined by your base cities. Have you selected them?

the 3 base cities for the "first timers" are usually Madrid, Barcelona and Seville.
What time of the year also makes a difference.

Ditto for danon's choice.

Blackduff

sorry, I just realized you said fall.
You may wish to fly into Madrid and out of Barcelona or the other way around.
Barcelona is more compact and easier to get around. Four days in Barcelona (relax, jet-lag etc), fly to Granada for 1-2 days ( just to see Alhambra), train or bus to Seville (3 days) , train to Madrid for 4 days ( trip to Toledo or Segovia).
or
Madrid first, train to Seville (Cordoba stop for a day), Seville to Granada, Granada to Barcelona.
Some people prefer renting a car - up to you.