I can only speak for the section south from Steamboat. First, if it rains, you will be dealing with thick, sloppy mud in several sections that can get stuck against your front fender and stop your tire from moving. Second, there are several sections, notably the northernmost stretch in NM that are very rocky, loose rocks, baby heads, I can't imagine doing this on a heavy street bike and not dropping it at least once. Third, there are a few sections with loose sand. Need I go on? If you want to ride it, go for it. There are people that ride the whole thing on GS's and V-Strom 1000's, it just not my cup of tea to take a street bike where it doesn't belong, wear myself out trying to keep it upright, dropping it and destroying lots of plastic, then taking a group effort to get it back upright. If that sounds like fun to you, that's great.
Talk to Raul, he rode a bunch of the East Texas and Louisiana rides on a DL650 and I think destroyed it. He's got a different bike now. Someone who knows the facts can help me out. I think the problem there was mostly mud.