It's kind of creepy, weird, and unusual. However, I can see someone building a distro and creating a bunch of non-OSS themes and basically selling the themes. That's not beyond the pale, although it is (again) questionably moral given that they probably created all of those themes using free software that they didn't pay for. But whatever.. just keep that in mind.
The usual way of commoditizing Linux is to sell service - so you get, like, 4 tickets a month or something where someone is guaranteed to be there to try to fix whatever problem you have within a reasonable amount of time, and you don't have to either rely on the kindness of strangers.
Zorin is mainstream enough that I suspect if they were really violating the GPL, someone would be on their case already. You can't - usually, depending on the license - just repackage OSS and sell it. So if that's how you wanted to spend your money, you do you and don't worry about the comments on this thread.
Oh, about your question: according to the upgrade page, the "upgrade" is just access to more packages, probably in another repos. You won't have to re-install the distribution, and there won't be any impact on your dual boot. You're just getting more packages to install.