Let's not forget Putin is at a net loss with this as he has still lost Ukraine it seems. Personally I suspect this is damage limitation - annexing Crimea or, more likely, reinforcing it as a part of his sphere of influence will be his priority because of the Black Sea fleet and will limit the basic geopolitial impact of the revolution
Also, the show of force created by using the military will act as a sign to other former Soviet republics that Russia remains powerful and influential, which is particularly important given the status of many disputed territories in the caucasus which may otherwise take any sign of weakness as a sign that they may also be allowed independence
It's essentially damage limitation - if he has to lose Ukraine he may as well take Crimea because he does at least have some sort of legitimacy to his claim even if some people would say it's spurious and this way he can keep the Black Sea fleet where it is and show Russia's power to defy the west to it's less tightly controlled neighbours
