A persistent server does sound nice.. if it doesn't provide too much trouble on your side, and we get a few more willing players.
Roll: If you're already lacking time, I'm not sure should I recommend it to you.. but anyway, if you ever find the spare money/time, you could give it a go sometime~
It's sort-of like an old-school 2D action-platformer, but with ability to mold terrain as you want (dig tunnels to make your own shortcuts, build an easy-to-traverse battlefield to make a hard boss easier), although there isn't a 'story' or anything, mostly just one big place where you can do various things.
It also gets steady updates with new content for free, so you'll get more and more for that single 10$ paid.
But still, as Bear said, it easily eats your time if you let it..