Last summer, I traveled around Spain by train and specifically for this trip, I bought a smaller suitcase with spinner wheels. I'm the unofficial chairwoman of the Traveling Sink Society and have been very unsuccessful in NOT bringing everything but the kitchen sink on my trips, lol! To make it worse, I like to buy books which are always heavy.
For the train, you must go light! Even if you line up early and secure a nice space in the luggage rack, there are still 2 more reasons NOT to schlep a 30 kg case:
1) Steps from platform to train
2) More steps up into the train
Altogether there could be 3-4 steps and unless you're Mr Universe, you will feel every add'l kilo.
Btw, I believe that Renfe's business class has a larger luggage compartment. Even if that is not always true, Spanish business people travel light so they hoist their small overnight cases onto the overhead shelf - thereby leaving the luggage compartment quite empty.