Got a 2012 Mac mini i7 ten days ago, maxed it out with a secondary SSD as a boot drive and 16GB of RAM.
With 16GB the maximum VRAM available is 768MB.
I'm using it as an iOS video game developer machine, and it's awesome. The i7 is really fast. I was surprised by the HD4000 performance, sure is slower than discrete card but it's pretty capable also for gaming. Diablo III runs very well with medium settings at 1600 X 1050, Portal 2 runs at maximum detail at the very same resolution.
I'm coming from a 2008 2.4 C2D MBP with the 9600M GT 256MB VRAM: the HD4000 on the mini is in another league, it's a lot faste for gaming too.
I have come from the same machine and could not agree more. League of its own in comparison the the 08 MBP's.
Also mine is showing up as 768mb of vram.