I wouldn't be so quick to undersell Syria's importance to Russia. Lots of people (not you) seem to write it off because "Russia won't fight us just to keep an airbase/port" and "Russia won't fight us just over Syria's oil". But most of them don't seem to have actually looked at a map, Syria is less that 400 miles from Russia, it's closer to them than Aberdeen is to London.
I am not convinced they won't fight (at least a small skirmish) to ensure they don't end up with Islamic extremists taking over a country so close to them.
Theres also the fact that they are trying to stop American imperialism in the region, protecting it's allies sovereignty is an important policy for Putin at the moment, it gives him clout in other neighbouring areas. While also being convenient for him in his ability to poke NATO enough into being the aggressor.