[glend (Glen)]

Alex, I think I know you and your situation, well enough to offer some advice. First, consider the weight of any purchase and your ability to manage that weight. Secondly, how are you going to house it (the new observatory I would guess), and are you thinking of a heavy duty EQ mount say like an EQ8 or CGX-L (If a newt, RC, CDK, etc)? Also think about putting your mount on a good pier, and now is the time to think about the footing, and make that part of the observatory planning.
Three, you don't necessarily need really big aperture to image effectively. A 12" f8 that you mentioned, I assume your referring to say a GSO RC12, the 12,5" Planewave CDK, or the CFF 300mm RC, would be the limit I would suggest in terms of size, and they are still pretty heavy, the Planewave weighs nearly 50lbs naked. Another thing related, try to buy from a local retailer if you can, and I note that Bintel now supply Planewave scopes, in addition to GSO RCs (And I know you like Bintel)..
Four, keep your present camera, because this will simplify the transition to a new setup, you can always upgrade the camera later on, learn the new scope first. However, as a caveat, maybe discuss with Bintel a package deal, of mount, scope and new larger format camera; surely has to be worth a significant discount if bought at the same time.
Five, are you a collector or a user? There are people who buy scopes that get used very little, if at all, and I won't name any. IMHO do not buy something you will not use, there are better places to invest your money. Telescopes are not financial investments, Although I will add that a good quality scope from a desirable manufacturer with a great reputation, say like a Planewave, will likely always attract buyer interest.
So those are my thoughts. You have my number if you would like to talk in more detail. Good luck.
Glen