You can get to Salamanca now on the fast train in less than two hours so travel time is a wash. Same with Segovia though there are more train options. If you're driving you can hit Avila on the way back from Salamanca.

Segovia is my favorite place in Spain mostly because I took my wife on our first date there but the castle on the hill and the aquaduct are pretty sweet plus the food was great. I would say you can't go wrong with either Salamanca or Segovia.

Regarding food. Check the Michelin guide for Spain. Outside of Madrid and the big cities the Michelin guide places are excellent and the prices are awesome. Terrible website but totally worth it.