I've dyed my hair black for years and because I treat it very, very kindly in all other respects, it's remained very thick, soft, and shiny despite doing my roots each month. I don't miss my natural hair color one bit and everyone I know agrees, black hair suits me best.
As for the vitamin enriched dyes and whatnot- frankly, vitamins ON the hair will do nothing for it. Your best bet in minimizing damage, if you do go for it with a chemical dye, is using one that's ammonia free.
Anyway, I think you should be adventurous and try it. If you decide you don't like it, you can always return to your natural color.
