The more I look at this E3, the more I like it. If I didn't already have one, I'd be VERY interested in this one. Claimed to be free of any major rust. Nice interior (new leather, uncracked dash, perfect headliner, good door cards, etc). Engine and transmission upgrade. All the hard to find Si trim is there and in good condition. Shoot, the tool kit is even still there and fairly complete.
Yes, it needs some body work and a repaint. For an E3 that means the new owner needs to be able to do the disassembly, most of the prep for paint, and the reassembly in order to keep the car within market value. It has not been driven much so it will need to be sorted out and "fixits" are going to be found. There are things like the "push to start button" that are already known problems.
The 3.0Si was the top of the BMW line up in 75 (well, there is of course the Li). However, for whatever reason it is the Bavaria that US buyers lust after. A 75 3.0Si is a bargain compared to a similar condition Bavaria (check Hagerty). The US 75 Si has the ugly bumpers compared to a 72 Bavaria (73 if you squint), but that can be fixed during the repaint if it bugs you.
The BaT gallery is going to spend most of their time pointing out the flaws on this car. I think that is a somewhat natural thing to do on any car that is for sale. That will probably go further to keep the hammer price low.
This E3 could be a diamond in the (somewhat) rough, and a bargain for someone that wants an E3 that doesn't have to be a Bavaria.