I have been wondering what has happened to my beloved Mitsui brand for quite a while now, and my efforts to scour the web for anything on the subject came up largely empty. I finally broke down and decided to find out for myself so I recently bought a 100-pack of their CD-Rs. If I learn anything worth mentioning as I use them, I'll post them here. I have discovered one thing already (more details below).
As far as your other questions: Here are some general ramblings and my own $0.02 based on what I know so far:
The only type worth getting is the Gold/Phalocyanine CD-Rs (the most expensive). Mitsui and Kodak were the only two major players offering this formulation in the past, and I considered them the only two which were better than TYs. I used these for long-term archival of important data, and for situations where portability, i.e. compatibility across a wide variety of hardware (both data and audio, especially older units) was needed. Commercial outfits like MP3.COM burned their music CDs for customers on Mitsui Golds (at least they did a few years ago.. I dunno whether they are using MAM-As or have switched to something else today).
The reason why I don't think their other formulations are worth getting is because I think TYs are better than them. This also applies to their DVD blanks. They don't use the gold/phalocyanine technology on them.
Now that both Mitsui and Kodak have pulled out of that market, the only real gold/phalocyanine player today is MAM-A who as you know bought Mitsui's technology license. We are therefore left wondering exactly what has changed for the better or worse.
Some disturbing signs include: (1) the posts which both you and I have read on the subject (2) Mitsui is on Plextor's recommended media list, but MAM-A is not (3) On the 100-pack of CD-Rs I recently bought, the edges of the discs have a wierd greasy green residue on them. Maybe it's no big deal, but I certainly wasn't expecting it.
On the other hand, some positive signs include: (1) MAM-A claims on their web page that they haven't altered the formulation, (2) MAM-A does sell a medical-grade version of their discs so they do meet at least some standard that's more stringent than the standard consumer market. If the quality really did go that far down, then they probably would be out of business by now from the first lawsuit over lost data to come along. This is just for CD-Rs, though.
Time will tell, though......