If taking several long-distance trains and wanting flexibility to change plans during your trip then look at the Spain Railpass which lets you chose which trains to take once there. Discounted tickets are invariably train-specific and can't be changed nor refunded I believe.

I agree that buses and trains are a better option to travel around in Spain. Once I rented a car and wasted a lot of time trying to find a place to park it in the center of Madrid. Never again!

2.5 weeks could be even not enough :). I spent a whole week in Barcelona and it was not enough for me because Barcelona has dozens of beautiful places to visit and has a number of free and paid tours. Most free tours offer a good overview of the city, while paid tours have more experienced guides who have a deeper understanding of their subjects. I tried some free tours and found a local guide, who showed me some incredible places in the city. If you like to meet locals and spend some time with them, I would recommend contacting this amazing girl: https://www.showaround.com/locals/ni...-spain-9581395. She told me so many unknown facts about Barcelona and Spain.