If a lens is minty and a low serial number, I wouldn't touch it. I've been eyeing a 50/2 on eBay that's #742156. #46 in the first series that could take AI rings. If I got it, I probably would put it on my F and leave it alone. But, my #748735 50/2 is currently in the shop, getting a NOS #3 ring fitted to it. It also needs to have the filter ring repaired or replaced with one that's straight. My 35/2 Nikkor-O did have a John White conversion done on it. Wound up putting a #34 AI ring on it instead. If AI rings are available, either NOS, or on junker lenses, I'm all for using them. That said, if I can't find a lens that I want and that will take an available AI ring, I will probably have a shop do a mill job. Not sure if I'd have him do it, since it seems like he usually just does a notch job and doesn't actually mill the ring all the way around, providing the EE post for the DS-12 EE Aperture Servo unit for the F2AS. My local guy (Doug at the Camera Clinic) does mill the ring all the way 'round and provides the ridge and the post. He won't, however, provide the lens speed sensing post. That was something that the late Brian Williams (microbee on eBay) did. He turned my old 28/3.5 Nikkor-H into a full AI lens that was fully compatible with the FG, FA, and F4, without damaging the cameras. Only charged $20 for that service, since I had already installed an AI ring from a 28/3.5 H that had fungus in the elements.
Most pre-AI Nikkors aren't worth much anyway when you go to trade them in, even the somewhat uncommon ones. When I've dealt with a shop, a mill job AI converted pre-AI Nikkor did net me more trade-in value than an untouched lens. A factory AI'd lens, of course, was worth the most of the three. Used camera shops usually don't care about "originality" unlike those of us who are collectors. They want stuff that's easy to sell, therefore, stuff that will work on a wide range of cameras, not just certain film bodies and low end DSLR's. Since, like ww12345, I'm more interested in using the gear than letting it sit on a shelf, collecting dust in a dying hobby (yes, we must face the realities that a lot of the next generation won't show interest in their grandfather's camera gear, no matter how well-preserved and original it is), I will continue to buy whatever pre-AI Nikkors suit my fancy and modify them as I see fit. Already did that with an 85/1.8 that was in pretty decent shape. Added probably $150 to its value by swapping an AI conversion ring I had from a very beat up 85/1.8 onto it. Bought the lens for $150, and, a BGN grade K-type 85/1.8 with factory AI ring on KEH usually goes for $330-$350.
-J
