So, since the majority of spiral knights is made out of textures, a retexture of haven would be simple, yet extremely effective and refreshing.

We could have night and day:
http://forums.spiralknights.com/en/node/48032

Seasonal changes, such as summer (current), winter (chrismas event), fall (orangy) and spring (flowery)
(Pittabread's idea from the same thread)

These seasonal changes could either take effect on a realtime basis, every 3 months that is, OR, they change on a haven by haven basis.
This would allow diversity between havens.

Say, for example:

Haven 1: Regular Summer Day Haven
Haven 2: Sumer Night Haven
Haven 3: Fall Day Haven
Haven 4: Fall Night Haven
Haven 5: Winter Day Haven
Haven 6: Winter Night Haven
Haven 7: Spring Day Haven
Haven 8: Spring Night Haven

And each successive haven would follow in this pattern.
Still thinking up more ideas for retextures...

We could also have perhaps havens based on dungeons
I'm looking through the texture files now to see what ones could matchup.