Actually, now that I'm looking at the script a little more carefully, it doesn't actually install anything, just puts the installers in a place where Wine can find them. So if you already have native .NET installed, you won't get wine-mono in your prefix.
If you're planning to install it, I'd argue that letting it install and letting winetricks remove it is faster than dismissing the dialog.
It seems it would make sense to continue grabbing all the stable versions as new ones come out, since old versions of Wine will look for the old .msi installers. Sorry I misled you earlier, Dan.