I've had the D-200 for a year and a half. I don't know how it will help you to get better pictures. It's a large, heavy and obtrusive piece of equipment (I repeat: L A R G E) and if you ask me not the best choice for night shoots the way you do them. Also, it has more noise then Canon at high ISOs. If you decide to get it, make sure you get a VR lens, it will give you 2-3 stops more exposure.

Seriously, megapixels don't mean anything unless you're planning to make print-outs of your portraits (web = 72 pixels per inch). Please aks a pro before spending your money on seductive gear... get a smaller camera, point and shoot. The D-200 has more settings you could possibly explore in a lifetime.