Sadly, our best shot for having knocked off Bingaman was with the late Colin McMillan in '94 (of course, had he won, and won reelection in '00, Richardson would've named a 'Rat replacement when he died recently).
As for Richardson, who is a repulsive, grandstanding, slimy piece of scum, I can't believe he has that high an approval rating (especially given all the neverending 'Rat scandals). Dendahl, however, may be a bit too controversial a candidate, and leans uncomfortably a bit too Libertarian (like Gary Johnson) on issues such as drugs (and you'll note he does have an unusually high disapproval rating, partly stemming from his tenure as GOP State Chairman). Of course, even with my reservations, if it's a choice between him and the Bill Clinton of Santa Fe, it's a no-brainer.
A few more politicians of Libertarian bent (personal responsibility combined with minding one's own business) would be a good thing.
That being said, I don't see Dendahl winning this year.