Well, how are you using it? Do you just want the budget worksheets, notes sections, ADR sheets for keeping track of them, and passpockets? If so, the old one will work just fine.
If you are using it for information, however, you are looking at a guidebook that was likely based on information valid in later 2009, then written up and published in 2010. A guidebook that is newly published is usually already a bit out of date, and every year that goes by makes it even worse.
There will be a LOT in that book that doesn't exist anymore, and a lot that's new that won't be mentioned.
Personally, I get the newest guidebook I can. I check out the Unofficial Guide to WDW, Birnbaum (wait, are those the same books? I get muddled there), anyway, I get all the newest versions of books out of the library, then I generally get the latest passporter. (though I'm starting to realize I mainly love the worksheets and passpockets so I might slow down with buying them...and I buy the refill pages anyway, because I have the Deluxe binder from a previous purchase)
On a non-Disney trip I took in the '90s, I was silly and read an out of date guidebook, and because of it got some fairly bad, outdated, information. It wasn't worth the savings at all.