I think, having seen what MF is really capable of, I should be sticking with it, at least for now. Right you are, cost is indeed an issue, especially at the moment. I'll never stop thinking about going LF now I don't think, and so one day it will happen! Thanks for your advice chaps
I might be wrong, but answering my own questions with the aid of advice from others is potentially part of the process, no?
Also, people might buy a TLR with a fixed lens because that is what they work best with... I bought the mamiya knowing that lenses could be interchanged and given the situation, would kinda like to take advantage of that. I think this situation is unique to the 'progress with kit once the kit limits you' argument, simply because I only own one prime lens for the RB as it is. With the sale of the F5, I could potentially get a 50mm and a 90mm to compliment my current 65mm. On the D700, I find myself sticking between 24mm and 50mm for landscapes as it is, so perhaps this is a good way to go?
Many thanks again to everyone for their advice, it's much appreciated!