Here's a diagram of the AVE rail lines.
Some of the day-trips you might take could involve the AVE or other fast trains that offer advance-purchase promotional fares; Girona, Figureres and Tarragona come to mind. You can save substantial money by buying non-refundable/non-exchangeable AVE/ALVIA/etc. tickets way ahead of time. Other trips could involve regional trains, for which I don't think there are early-purchase discounts. You can explore train options on the Renfe website. It's always worth looking at the trip duration and price, because sometimes there may be a substantial price difference for a train that is not all that much faster.
I didn't use any train passes in Spain except for the senior card, so I don't know whether there's something available that would fit with your plans.
You may find buses helpful for some destinations, as well. I always check Rome2Rio.com to see whether perhaps a bus would be faster. If that looks possible, I drill down until I find the name of the bus company and--with luck--a link to the schedule. Buses are usually cheaper than last-minute tickets on the fast trains, but in that situation the bus will be quite a bit slower.
Enric created a detailed thread about visiting Montserrat from Barcelona not too long ago. You'll find it easily by reviewing the Spain forum here.