You are right! In my opinion, the Arcade VGA paired with the D9200 is overkill. Plus, you can't get any of the 25khz games to display in their native resolution. Why spend $100 when you could spend under $30 and get a Trident Blade T64, or a Matrox Millenium G400 for around $15? The Arcade VGA card is for people that want to use Mame32 with their D9200, making it easier to run (as opposed to AdvanceMame), but you lose the true 25khz emulation.
For perfect unmatched emulation, make the extra effort and go the AdvanceMame/T64 (or equivalent)/D9200 route. I just think buying a D9200 and running anything other than AdvanceMame is a waste of money. AdvanceMame is the only way to harness its full potential. I mean, if you are planning on running Mame32, why even bother with the D9200 or Arcade VGA? Save your money and buy a cheap PC monitor instead.