I'm having similar issues with a VX2245. Since I purchased my mini, it's had issues determining resolutions, holding a correctly detected resolution, and frequently just getting a display to show anything at all.
Recently, I swapped from my 4th DVI cable to the VGA adapter that came with the mini. Now it seems that the display appears at every boot, which is very nice, but not in the monitor's native resolution. Instead, it insists that I need 1600x1200@60hz or 1400x1050 at 75. If I'm not mistaken, "correct" would be 1600x1050 @ 75, which I've gotten on and off across the last year.
I think my current recommendation is to bail on the viewsonic, although I have to admit that the mini ALSO has trouble with 4 other brands of monitor. I was hoping Snow Leopard would have some back end driver magic, but that was false hope.