HI Guy
I know your question was partly flippant, but I'll take it seriously, and, since you ask, I'll tell you why not.
The reason is simple, there isn't any shooting I do where I really have the time to stop and think, to shoot deliberately - the reason I get my landscapes is because I've climbed through hedges and ditches and got there, the reason the natural close ups work is because I'm shooting with continuous autofocus to take into account that the damn subject is blowing about all over the place. The reason I get employed by the BBC to do radio presenters is because they like the candid work I do in natural lighting - with people moving around fast in changing light.
Even the still life shots I do indoors are ALL handheld, unarranged and in natural light. The minute I start trying to formalise the situation the life goes out of it. I haven't used a tripod for anything other than testing lenses (which I always do by the way) for at least 2 years.
The only thing that MF would do for me is to give me better image quality for a much fewer number of shots in a smaller number of situations. I also know myself well enough to know that I just wouldn't take it out with me when I was walking (too heavy to get a representative number of lenses).
As for just having MF and the M8's - not a chance - I had a church jazz concert to do a couple of weeks ago: I couldn't possibly have set up a tripod in the circumstances, the lighting was dreadful and most of the shoot was done between ISO 5000-6400. If it had been paid, I would simply have refused, but it was for a charity. The pictures were used for local papers and will be used by the conservancy body. The M8 would have been lovely - but I wouldn't have had a prayer!
church shots at high ISO
So, I can't just do with M8 and MF, I need a dSLR - the D300 is no good to me because of the problem with quality zooms at sensible ranges. So I'll have to put up with the D3 until Nikon make a smaller FX camera.
I was so close to buying the Mamiya (as you did) at around the same time, but I realised that although I really WANTED to go MF, there wasn't a single situation I could think of where it would do anything for me except improve the image quality . . . . and I'm not getting complaints about IQ from the M8 or the D3 - what I want to improve is the IMAGES, not the dynamic range or the resolution. Money isn't the problem, and nor is the size. As for the 'no 24MPX Nikon or Canon will match a MF system' - well, you may be right, but it's tough to write Nikon off before it appears, I think everyone was pretty surprised by the D3 (but not the D300, good as it may be).
I'm as much of a gearhead as the next person (more than most), but I have to keep telling myself what we all know:
1. nobody ever liked a photograph BECAUSE the IQ was good
2. nobody even THINKS about the IQ if the image is fabulous.
I need the kit which is going to get me the best image, not the best quality image