Sad, but I am afraid I agree with you. Romney the chameleon will do better with actual primary voters than the polls indicate. The history is clear, GOP primary voters default to the safest option more often not - especially when the alternatives are so weak or untested. Newt or Cain might win in Iowa, but the pattern will establish itself pretty quickly in the rest of the states and it will follow basically along your predicted outcome.
The best we can hope for it Newt really gets his act together and grows into a very strong anti-Romney candidate. If the majority of movement conservatives and Tea Party folks get behind Newt early enough, it might change the dynamic.
I doubt I'll vote for either in the primary. Probably will either toss my vote away or not bother to show up. But if it's clearly a choice of Newt or Romney when the primaries hit NJ, I'll have to think about it.