The way the icon limit increases is a bit confusing...I think they give you 15 for upgrading and then more for consecutive months of paid time or buying a whole year. I did a one-time payment for a year and I got 25 extra userpics total. The other things I like are editing comments and comment tracking.

I started editing the last one and realized that when you crop and resize it, River ends up looking like a Muppet. Her face is sort of squished behind Eleven's and it looks funny at icon size--sorta round and featureless.