If things are working fine and you are not up to the minor challenge of upgrading the OS, then stick with the 2gb card which holds a good deal of songs and pics. If however you want to store an insane amount of media and you trust your ability to follow the easy directions given on this forum then dive into the upgrade pool... I did..
Keep in mind that most problems you run into can be resolved with a few minutes of searching and posting right here. So if you go for the upgrade and an error pops up, don't panic, just log in here and these guys will get you going.