I have next to 0 experience with metal snares, but when dealing with VST instruments, be it drums or whatever, I always end up adding noise to the tracks to make the sit better. It can be from distortion plugin-thing, one of those 'vintage' style plugins which have way too much hiss/noise, or more often than not either Waves' tape machine or running it out to either my ancient dbx 118 or to my 'gold mike' preamp and turning it all the way up.
I've always added noise without really thinking about why...it just made it site better. I gave a little thought to it when answering this thread and my conclusion is that most of the other tracks are recorded in less-than-ideal rooms, with less-than-ideal equipment and occasionally even less-than-ideal background noise.
VST instruments on the other hand are recorded in AMAZING rooms with AMAZING equipment. They sound absolutely pristine and are recorded to fill your speakers (when generally you just want them to fill a space in the mix). So I must be battling to make them sound as shitty as the rest of my tracks :P