Yes as Aengus said it is kind of like making a bet and hoping you win.
If you buy all the stuff now, you have it, but you have less credits to spend on the Halloween items.
If you don't, you don't have the items and you hope that you can still get them after Halloween ends. However, you can still trade for them, but by the time you go to get a deal through, they might retire them, and the person might want more than what you would have originally paid. (By the way if you choose this plan and it fails, see me about a deal, because I bought two of everything.)
Personally I hope it doesn't stay, because I would like to see new stuff.. However, if yavn surprises us when he adds all that new stuff next week, that Tron stuff may be there for another purpose. If you have no clue what I am talking about, it is the second half of Tomorrowland.