If you want a better High ISO...the 1D2 is excellent and doube the megapixels. You can find it for 600$. IF you consider selling the 1D, its doable.
If you think you could like more reach...the Pipe (80-200L f2.8) is a marvelous piece of glass.
A good shape used one can be found for 600$ also...if you have the pacience to look.
I'm probably getting an UWA myself once my B&H refund of the 135L goes through (decided to keep my 70-200 over it). For me at least, UWA is some of the most fun to shoot, especially with a close-focusing lens and lots of UWA focus pretty closely.
Well, I decided what to get. I'm going to save a bit more for a 200 2.8L and maybe a 17-40. I'll have to live with what I've got for a bit longer, but that's ok... I'll suffer
- your current lenses are doing just fine 
