AFAIK, the "original" AN/PEQ-16 was not used in any real numbers outside of testing and evaluation.
The first widespread use of the '16 series was by the Marine Corps in the AN/PEQ-16A form, with an incandescent white light. The AN/PEQ-16B, as you noted, received an LED upgrade.
Again, to my knowledge, the AN/PEQ-16 series is not in any kind of wide use in the Army or in USSOCOM, the Marine Corps seems to be the primary, nearly exclusive user on a general basis (though this is not to say that they have not been in limited use/purchase by other branches).
The Army is more or less "standardized" on the AN/PEQ-15 (Insight ATPIAL) and the AN/PEQ-15A (LDI DBAL-A2) for individual weapons, while USSOCOM continues to use the LA-5/PEQ family (Insight ATPIAL).
I have not personally used any of the AN/PEQ-16 family other than to finger-fuck them, but I have not heard too much positive about them other than the fact that they have a relatively small footprint for the capabilities. This is not to be understood that they're horrible or unusable - but most folks I've talked to seem as though they'd prefer a separate ATPIAL and WLI module, rather than the PEQ-16's "one stop shop."
As for whether or not Insight will still service them - assuming that they accept and approve of the chain of custody, and would agree to work on them at all, my inclination would be to say that they would prefer not to support this model, and would try to upsell you into AN/PEQ-16Bs. I have no inside information regarding that, so that'd just be my guess, take it for what it's worth.
As far as what they're worth... ::shrug:: if you're talking about buying them as an agency, if you could get them at a good price relative to an AN/PEQ-15, I'd pick 'em up. No reason not to, particularly if you're budget conscious. They'll do everything the ATPIAL will, so if you can get them cheaper than you could get ATPIALs, I see no reason not to. I wouldn't pay too much of a premium over what you could get a '15 for, though.
All current Insight compatible remote switches should work for them, and IIRC, the mount is an integral rail-grabber, just like on the ATPIAL.
No clue about the white light upgrade, but I wouldn't be optimistic. The pattern generators look like they'd be compatible with the ATPIAL, and I would assume that they were, as it would make the most sense, but I couldn't say for sure.
~Augee