Hiya. I used to play this game all the time, but after Grey Havens took over and the release of the new Vanguard missions I started to phase out of it. Have any major changes happened (e.g. quests, floors, drop rates)? Do we have any news on any upcoming updates? Has Grey Havens been more responsive than Three Rings?
The patch notes are sadly sparse as always so they're not much help.
I loved this game and I'd hate it see it disappear.
You are right that the patch notes (on the wiki at Release/all) are not updated anymore and hence sparse. For recent changes, instead read the Announcements forum.
The only big change, since the rank missions you mentioned, has been the sleep update, with new monsters, equipment, and levels:
http://forums.spiralknights.com/en/node/117900
Grey Havens has been more responsive than late Three Rings, but less responsive than early Three Rings. They have their hearts in the right place, but their resources are very limited. So you should not expect lots of new content.
All online games gradually diminish until they are shut down. I've been hearing about the disappearance of Spiral Knights since 2011, and it's still here. My recommendation is that you enjoy it for what it is (if you do enjoy it) while you can. Cheers.