Moving up from SLT-A55

I'm new to photography but since buying my first decent camera a year ago I've learnt a lot. I've got the A55 with 18-55 kit lens and a cheap 70-300 Sigma. I'm now keen to move to something with significantly better usability (the A55 is a bit fiddly to change settings quickly) and much better image quality particulary in low light use. I'm getting the hang of better composition but am frustrated by the poor image quality i'm getting. The options I'm thinking are

1. Buy some decent lenses (doesn't solve the usability problem)

2. Upgrade to A77 and buy some decent lenses

3. Switch to Canon and buy a full frame 6D (and some decent lenses)

I'd like to go full frame Sony as I'm used to the benefits of SLT but it's too pricey. The image quality at high ISO of the 6D looks very attractive. i appreciate this forum isn't going to tell me to switch form Sony, but it might tell me why I shouldn't.

Does anyone have any advice about option 2. Would I get much better image quality from the A77 and how would it compare to the 6D?

Phil.