From what I've seen, drank, and brewed, I think 0-8% Munich is safe for American IPAs. But you could certainly use 9-15% if you like what it offers. Same principle for cara- malts. I prefer both of these malts to be at the lesser end of the spectrum in my American IPAs, but it's all about personal tastes. Depending on the recipe, use of these malts in higher amounts may lend a sweeter, fuller, toastier, maltier, bready, caramel traits to your beer. Use more than is typical if that is what you're after.
Wheat is a little more common in hoppy pale American ales. You can keep it under 10% for head retention purposes or stretch the limits of its use without adding sweeter toastier flavors, while eliminating cara- malts altogether in both cases. I believe Lagunitas A Little Sumpin' Sumpin' uses 50% or more wheat (in three different forms). And Lagunitas Sucks uses wheat, oats, and rye in addition to 2-row.
All in all, it depends what you like. But will I prefer to see the beauty of unbalance in American IPAs as it pertains to malt backbone vs. hop character. For me, it's all about the hops... their aroma, their flavor, and their inherant bitterness. That's not to say you should be left with a harsh watery bitter mess of 1.055 OG and 300+ IBUs. But a close balance of malt and hop flavor should technically not be what you are striving for this style. A good tip for adding subtle malt character while not overloading on specialty grains or the darker Lovibond malts is to use English 2-row (or a half English/half American 2-row blend) and/or English yeast with American hops.