To me, the spectrum of Crystal malts (very generally) goes from honey to toffee to caramel to raisin/fig, while Munich malts have a spectrum that is more like progressively darker bread crusts, with Aromatic malt being the darkest end on that spectrum. You can certainly try substituting some Munich for Cara-malts in a recipe, but the result will likely be much different.
Also, add me to the camp that doesn't find that Caramel malts make sweet beer. I have a funny feeling that this is an old brewing myth that dates back to when a lot more brewers were using extract, and possibly poorer quality yeast. Yes, C-malts have flavors that are reminiscent of sweet things, and that would be accentuated in an underattenuated beer, but they themselves don't add much sweetness directly.