I prefer not matching but I also don't like an even number of things either.

For instance: I have one tall dark bureau, one shorter bureau that I painted w/ grey stripes, 2 matching bedside tables in a lighter wood finish (oak? pine? - not sure) and a black wrought iron bed.

I'm considering using my current bedside tables for sofa end tables and using my mismatched side tables for my bedside tables. They are mismatched but both painted the same cream color.

Matching end tables will give you a more formal look, where mismatched is casual/eclectic as will matching, but different finishes.
It sounds like you may need to add a little "brightness" to the room. If you go with a wood or black finish, maybe add a metallic edge. I do better with pitures, but my gut reaction is matching, but not black or dark wood.

I like for the color of all the wood to match, so I'd match the wood IF you get wood nightstands, match the black iron IF you get iron nightstands. :0) A little bit of a hodgepodge is good....it could end up looking like clutter and disorganization. A little symmetry is nice.