Given my druthers, if still doing production on analog tape, I'd find a clean MCI/Sony 24 track.
I drool every time I check out the Mara Machines. On the expensive side, but you know where the money went.
Home - Mara Machines
There was a guy not too long ago selling a 2" 24-track...and I looked at it hard, it was "new" from, Mara...and he only want like $7k for it, which is a great deal instead of the $12k...but then it was far away, crating and shipping w/insurance would have added at least another $1500-$2000 depending on the carrier.
It's not that I'm unhappy with my Otari MX80...but you're right, the MCI machines have that "mojo" in the electronics, just like some Ampex machines, and you do get some "color" out of them.
My MX80 is on the more neutral side with its electronics, though I can still add some flavor with the tape choice and how it's setup...but that also allows me to add color before and after the tape.
If I sprang for an MCI...I would probably keep the MX80 too...because it's actually more reliable than a used MCI, though the Mara machines are probably in another class, because they are fully refurbished and tested.
Back in the mid-90s, I did a short stint at a local studio that was pretty decent...not your million dollar studio, but they had a Neve 8058 and also an MCI 2".
I remember one sessions over a few days, that MCI kept "throwing a shoe" every 20-30 minutes of use...it was some small part that was blowing when the machine got hot, but it was a generic part, because the engineer had sent one guy to the local Radio Shack and told him to pick up everything they had on the shelf of that part (I wish I could remember what it was...but it wasn't a fuse). So when it would blow...it would take him maybe 5 minutes to replace it, and back to the session.
Not a major issue...but the one day, it was getting late and there was only one replacement part left...so if the session went longer, you would have to stop.
I know that doesn't paint a complete picture of reliability issues...but I know they were temperamental. The other issue with it was the remote....maybe it was an older one...but he had to literally PUNCH in hard-n-fast on the switches, otherwise there would be a noticeable audio glitch.
All that said...if I wanted to throw down the $$$...I wouldn't have any other reservations about getting a Mara MCI. They just do MCI desks and decks. I almost bought an MCI desk from Chris Mara, but it turned out to be too big for my old studio space. If it was now...I could easily fit it into my new studio space.