I'm a regular BART/folder user too. Rolling has been discussed here many times but it doesn't seem to be a key feature for most. Unless you have a physical condition that forces you to need to roll or have really offbeat commute hours, I don't know that rolling is all that great an asset. I spent a lot of time learning to roll my Dahons but almost never have a really need.

Stations are often so overcrowded that carrying the bike is a lot more comfortable for me. It takes up less room on the platform and is easier to navigate crowds carrying it. You are allowed to take your folder on escalators and elevators, so there's really not a huge amount of carrying required (although I can use the workout and prefer to haul it up the stairs). Just make sure you have found the most comfortable way to carry your bike.