If your monitor is in good shape (I assume it's a standard CGA monitor?), I'd probably stick with it. In my experience, here are the areas where a multisync would be better:
1) vertical games of 288 lines or more (256 line verticals still look great on a CGA though)
2) medium resolution 512x384 games (there aren't too many)
3) windows desktop with no flicker (front ends at 640x480 look fine on CGA)
4) PC games that need 800x600
So really just ask yourself if those things above are worth $369+$110 shipping to you.

The other emulators you mentioned all look perfect on a CGA monitor BTW.