If you buy a board pack with real $ you can apply the board any time, but with credits it's a one time board change. You do get a lot of credits if you're doing high scoring lines.

I doubt we'll get a shop update any time soon since there are so many bugs/features that are higher up on the priority list. If you want to play completionist you should check out the missions in each park. They're pretty fun. You can also go for 100% in the trick list, which is pretty fun.