Well, you went and bought some paints, right? You must still be doing some modelling of some sort.
Nothing TOO drastic has changed in the last 5 years on the model-side. What army(ies) do/did you play then? If it was Grey Knights or Necrons, and you want to pick those back up, thats one thing. The line has been re-done or updated quite a bit. If it was Space Marines, then a Space Marine is a Space Marine is a Space Marine. Not much needed there. Eldar? You're in luck..nothing new has really come out lately.
Whether you need an update or not, there's always cheap ways back into the hobby. The Swap Shop here or Bartertown always has people selling off stuff at VERY reasonable prices. I like to think of it as continuing my hobby off someone else's broken dreams

Ebay is always an option as well. There's never a reason to pay full retail.
As far as the upcoming edition change goes, no big deal. You could wait the 6-7 months or so until then, or you can get some gaming in before that. Perhaps take the time to start updating/painting the models you currently own, then when 6th edition comes out, take a look at the rules, play some games with what you have, maybe proxy some stuff in friendly games, and decide if you like it or not. Very little money spent then until you are SURE you're enjoying it again.