Should I upgrade my Nikon to a newer model?

I'm on my second year of doing portrait photography and I'm in need of either updated gear or additions to what I currently have. My camera body is a Nikon D100. I have a 18-55mm, 55-200mm, and a 50mm f1.8 in my bag as well as a sb-50dx speedlight. As you know my camera body is an older model with only 6mp. I don't really have any problems with it, but I have noticed in RAW, after taking 2 quick snaps there's a shutter lag on the 3rd (I hope that makes sense.) I'm debating on investing in the nikon d800 or adding to my gear. I feel I'm not getting the sharpness I would like to achieve. In your experienced opinion, would the switch be worth the money? Would I see enough improvement in my photography? Do you have another suggestion on a different upgrade that isn't so costly, but gives better resu

If you are opening a portrait studio, then it could be worthwhile to invest in FX and professional grade FX lenses. If not, go for the D7100.
Despite some people calling the 50mm a portrait lens, there's a reason that in the film days no one was making a 75mm portrait lens. Worthwhile portrait lenses include the Micro Nikkor AF-S 60mm f2.8 or the Nikkor AF-S 85mm f1.8. Or the Sigma 70mm f2.8 macro.
Your SB-50DX could be adequate. A new SB-700 would be nicer. You need a good tripod.