To be honest, if by "full upgrade" you are referring to Logic Studio, I'm not really sure why you are even considering it unless you find a really sweet deal and want Soundtrack Pro, Compressor, and Waveburner (which are discontinued.)
Otherwise, why not just get Logic Pro for $200 from the App Store, and maybe add Mainstage for another $30 to get all the jam packs. Then you will be eligible for future updates and upgrades as Apple are now selling their software via the App Store as downloads. Since Logic Studio is discontinued, if you buy it somewhere you will have no future upgrade path . . . in other words, if you want Logic Pro 10 whenever it comes out you will have to pay full price for it.
But then again, who knows? Since Apple have just made the transition to digital downloads via the App Store it's possible they might make a one-time upgrade offer to LP10 for current owners of Logic Studio. One can only guess.