I think Putin was justified with the intervention.
Ukraine was leaning strongly to wanting to become a NATO member, and we are probably stupid enough to let them ,,, And it doesn't take a strategic genius to figure out why Russia doesn't want a NATO state in the heart of its country.
I think they are playing the aftermath wrong though, no one believes this "referendum" is going to be anything other than an annexation done at the point of a gun. Putin should just say "We did what we had to do for our national security, deal with it !" And so long as he makes no more aggressive moves it would all blow over in weeks. Now hes trying to justify it with a rigged vote, no one is going to recognize the results, and things could get ugly.
As far as Russia tanking the US dollar, let him go ahead and try it. Certainly not the 1st time anyone has thought of the possibility including Iran, Saudis and China. The reason they don't is because they would be cutting off their left foot to save their right - There is nothing viable at the moment to replace the US $ as a peg for international transactions, else people would have been using it long ago. People still see security in greenbacks [for some odd reason] ,,, And as long as that remains the case, threats like this is just bluster - Without their gas on the markets, Russia goes back to being wheat farmers ,,, And without a flood of slave labor produced junk, China goes back to being rice farming peasants.
Yes, we would feel some pain as well, but if we are eating bread, they will be eating dirt and they know it.