Train from Porto to Lisbon; Bus from Sevilla to Granada: Buy Tickets Now?

Online they appear to be 39,50EUD each for first class on the faster trains (~2h40m). It looks like there shouldn't be a problem with picking them up in Porto.
I'm guessing the bus tickets won't be a big deal either, unless someone knows something more. In Rome, we were only a few blocks from the train station, so getting our tickets was relatively convenient.
Regarding the train, how much difference is there between 1st and 2nd class for this trip?
Thanks all.

I splurged for first class, as I was hoping there would be room to spread-out. But the car was completely full. Though they did have free sandwiches and beverage service.

I took the Porto - Lisbon high-speed train back in 2004. I had no problems purchasing tickets 30 minutes before departure. There are automatic ticket machines which are very easy to use. If you wish, you can also purchase your ticket at the station in the center of the city if you happen to walk by it. For Lisbon, you have a choice of using either Oriente or Santa Apolonia stations. SA is located very near the city center, but is not connected to the metro so you will have to use a taxi to get to your hotel. Oriente is quite a distance from the city center, but is connected to the Metro. Neither station has lockers or luggage hold facilities.

I agree that you should not buy the Porto to Lisbon tickets ahead of time. About 7-8 years ago when we did this run, I found that the local prices were almost a 1/3rd of what was on rail europe.