This is a familiar issue to me as well. 2 cents worth:
Originally, MF was a midway point between LF ad 35 mm, offering close to the convenience of 35 mm, but with enough film size to get a significant quality difference, more akin to 4x5. Not exactly fast, not exactly slow, somewhere inbetween.
I for one loved that - and carrying a TLR or MF SLR gear was worth the specialness. If it was a long day, the TLR was the way to go.
Now, with the digital backs, the whole equation is turned a bit goofy: the image quality of the smaller cameras (Leica for example) is much higher, and hard to resist. The carrying of a MF camera with a back is tedious all day, if not hard, and we're all getting older. So why MF digital?
The first reason is quality and control. I have a Phase 20 back on Rollei gear, and it has changed the way I shoot; not nec. for the better, just different. The camera is happiest on a tripod, and is the finest, fastest studio camera. I get great composition and wonderful files.
Out and about is less flexible: it needs good light, but takes wonderful shots. I can carry it around for a couple of hours, but not easily all day. Would a Hy6 be better? Yes, but the Sinar back is still a bit large - the Leaf is better.
The reality for me is that I still like the MF shooting experience: more control with the WLF, better composition, more keepers. That said, the M8 still gets most of the use, but as aligning the camera parallel to the picture surface remains so hard (and easier with WLF and MF), I'd rather have the MF setup.
Thus, I'm stuck on this one. Laying out massive cash for the sheer pleasure (expedience) of a better finder and better control is a bit silly. On the other hand, it does matter, albeit only for that and maybe the occaisional super large print. Otherwise, its hard to argue for it.
Still, I love the older stuff and those big lenses. But I went to shoot a building being wrecked this weekend and put four lenses in four coat pockets with the M8. Hard to argue with that!
Geoff