[jules]

I just read over this thread here which says if Apple hasn't introduced a whole separate version-upgrade method, that I would have the option to buy the upgrade from the Omni store. So it seems it's up to Apple as to whether I can stay within their App Store and still get upgrade pricing, so far it's not the case. New version, new full-price.
Also later in that thread it says buying the MAS version could have some untended side-effects such as not being able to run all the scripts posted on these forums because the "bundle identifier" is different in the MAS version. Hmm...

Update: Scripting workaround here for MAS-purchased OF.

I'm going to have to think about this and see. Since I have to buy the iOS versions on iOS App Store, I wanted to just make it all a clean purchase and use Mac App Store. But it sounds like the better path is to just buy the Mac version direct?