I would take the other side and say do it. Sell! If you are not happy using the gear, there is no point hanging onto it. There is of course a period during which you need to get accustomed to gear before you know if you really like it, but it sounds as though that period is long gone for you. If it is a struggle to enjoy it and get the results you want of out of it, there is no reason you should keep trying to push that boulder uphill. You have the M9, which is a wonderful camera capable of producing excellent large prints, as is the Mamiya 7 and the Toyo 4x5. I can't imagine their quality not being enough for any standard application...I am not sure if you are a working pro or not, but if not, the client side of things should not be an influence. Just go with your gut...
Stuart, that is precisely my sentiment. My main income is not from photography, but I do some jobs. One of my businesses is a large format fine art print lab so repro work features in that.
There's more to this story. I was sold 2nd hand gear as new by the local dealer and very very poor service until Alpa HQ stepped in and sorted it out. Almost all photography dealerships in HK/China seem to be run by Clowns'R'Us international Ltd. Pulling out all the packaging from storage yesterday, I realise I never really got over it all (or maybe knowing this has cost 1'000s of $ rekindled the flames), I still feel very bitter.
I now have some trusted dealers overseas, so pay more and ship everything in. Without a good dealer this gear is a minefield and has cost me far more in the long run. My main point here is find someone you can trust, or just stick with the good guys who have earned a reputation. It's hard for small companies like Phase or Alpa to know what's going on in the world, so the dealer is critical. Select him/her as you would an employee because they're like an extension of your business and could easily ruin it for you.
All said and done, it took at year to learn that hard way what is right and wrong for me. In the end it comes down to that. That's why I post this here, in the hope that it might help someone thinking about technical camera's can benefit from the mistakes I made.
Phase One are one of the few who have a presence in HK (most companies use distributors). I hope I can conclude this by sticking with my IQ160 and switching to a large format camera with sufficiently accurate movements. And hopefully Phase/Mamiya will come out with their new SLR soon.