Been tempted to start making some addons as well. I'm not bad with meshes, but as my knowledge of aerodynamics is quite basic and I lack the coding experience required for making a decent ship, I think I'll be starting with something easier.
I have plans for a surface base for Jupiter's moon Io inspired by Peter Hyams' Outland, and an UCGO rover along the lines of
this
Then, if everything goes alright, I might move to more complex addons.
I've been changing jobs recently, though, and what little free time that leaves me goes to friends, family and learning Orbiter's bare basics. Maybe in a couple months I'll get to it. I'll tell you all in the addons forum then.