I'd just keep what you have.

200 lbs total weight isn't too bad, but as I start adding weight to my Colnago, I start feeling some flex in the rear-end... I think, although I haven't ever really determined the source.

You could go for stiffer rims with more of an Aero/Arched profile.

The other thing that I've read is that most people consider double butted spokes to be just as strong as the straight spokes, perhaps even stronger as they have some stretch where you want it. So, if you don't have butted spokes, you could rebuild your wheels with better spokes and rims. I'm not sure about light alloy nipples. I'm just starting to experiment with the alloy nipples, but you can save a few grams of rotating weight.