Graphics card performance IS starting to make a difference to Mame now that the Devs have started to offload some of the rendering to the GPU. As the newer internal Mame drivers start to appear in the next year or so, graphics card performance WILL start to make a difference to Mame performance.
That would certainly be nice if true. Just curious, where'd you read that? I've always heard the mamedevs say that due to the non-uniform nature of graphics hardware and APIs, they render everything in software (CPU) and then just use the GPU to copy the single rendered 'polygon' to the screen.
The card can make a difference, but
not because mame will let it emulate the game's rendering. (ahofle, you're right about how mame does the video.)
Mame now uses direct3D by default, & some directX 9.0 stuff to display overlays & bezels. Mame still emulates the graphic calulations in the CPU, but can offload the final rendering to the card (mostly the overlay & stretch to screen).
Basically, a card that does directX 9.0 in hardware, has nice d3d, and (optional) clean s-video out is all you need. However, a semi-new card that does directX 9.0 in software, or older that can't do dx9 or dx8, or does d3d in software, or an onboard chip that shares main memory, can be noticeably slower than a good card.