Creator updates not showing up in My Purchases?

AFAIK buyer doesn't get notifications about updates on model, but he can download purchased model at any time. I think he can download model even if it was removed from marketplace - i had one such case where i saw download of one of my model, several weeks after its removal.

In a normal scenario those download buttons would just be links to the same database entry, it would be very inefficient to store multiple copy’s of the same thing.

So no other page for updated models needed, just replace the database entry (your upload).