Well I've got two of the three so I can understand your contentedness

You answered one of those spam adverts and the miracle growth formula actually worked?

If they bring out a silver DA35 Ltd I'd trade it for my black one...

I don't remember ever reading any horror stories about the 12-24, mine certainly seems sturdily built (and happens to be wonderful) so I can't think of any reason to avoid a used example.

That's a very rare camera in black! Certainly had some parts added from a silver version though - I see the lens standard, base plate, self timer lever and film winder all out of place.

I bet if you put it on eBay though there'd still be a collector willing to pay a pretty penny for it as it stands.

A direct comparison between the Pentax and Mamiya MFDSLRs probably isn't fair as they are aimed at very different photographers. If I wanted a studio workhorse I'd probably go for one of the Mamiya options, whereas the Pentax makes much more sense as an all-rounder, especially out in the field. If I needed access to service centres at a moment's notice anywhere in the world then a Hasselblad would probably be worth the extra money. If I was a Saudi prince or Russian oligarch with money to burn then I'd buy a dozen Leica S2's for the snob factor and pay someone else to go and take the pictures for me...

Pentax is still cheaper than the *equivalent* Mamiya. From your link:

Pentax 645D body only (includes 40MP sensor) $9,995
Mamiya 645DF body only (no sensor) $5,990
Mamiya DM22 body + 80mm (includes 22MP sensor) $9,995
Mamiya DM28 body + 80mm (includes 28MP sensor) $14.990
Mamiya DM33 body + 80mm (includes 33MP sensor) $19,990
Mamiya DM56 body + 80mm (includes 56MP sensor) $32,490

The standard Pentax lens usually adds around $1,000 to the body price, giving a total price of about $11k. In Mamiya terms it would slot in between the DM33 ($20k) and DM56 ($32k), making the price of a 645D look almost like a giveaway!

Some cheap extension tubes should have both male and female bayonets.

I think Sir would like a Leica S2. It has a similar sensor to the 645D (same physical size, both made by Kodak, "only" 37MP though) and weighs in at just over £20k body only. You really don't want to price up a set of lenses to go with it though - it'll cost you more than a nice house.

Medium format does give incredible detail, enhanced dynamic range and a huge improvement in tonality. As others have said though, all this is pretty much wasted on images seen at screen resolution - you really need to see prints (big ones at that) to fully appreciate the differences. If you're a fine art photographer getting paid £000's for limited edition gallery prints then it's a no-brainer; for the rest of us mere mortals it's harder to justify, but if I won the Lottery this weekend...

At my local auction house I'd expect to pay around £30-40 for that lot. Much cheaper than eBay of course but nowhere to turn if it turns out to be broken - auctions always involve a bit of a gamble.