As you have noticed, most of the time tantalum failures occur with 16V rated capacitors on either the 12V or -12V lines. Those are the only cases I would consider for preemptive replacement with 25V caps, mostly on 80s or early 90s stuff which is where the explosions usually happen (IBM stuff in particular seems to be greatly affected).

IMO If it's working now and you run it semi regularly, there's not really that big a chance of a tanty blow up, it's when they sit unpowered for years. So if you're thinking of replacing tantys and leaving it unpowered for years, guess what, yup, still a chance one will short and pop. So pretty much it's a thing to do if there's an untouched for decades precious system that has known delicate unobtanium chips before you power it, as insurance... but if you took the risk and it runs, no point.

Edit: BTW I think the ESR goes worse with voltage rating on these, or at least did back in the day, so going to higher rating means more current consumption on the board, not a biggie for one replacement as required, change 50 of them out and you'll notice.

Well, some of my systems I'm working on getting back into service. But I also have some that I haven't powered on in a very long time. Including a PS/2 system I recently was given. So I may look for any tantalums on the +/- 12V and see about replacing them.

Thanks for the info about current consumption/ESR. I think a lot of these old boards I've looked at only have maybe one on each of the +/- 12V lines. Not sure about the PS/2 as I haven't had much time to dig further into that one. Plus that one has the 3 legged tantalums....I had to look up about those, first time I had seen one. Seems they still exist in some form though so shouldn't be unworkable.

I know on the PCjr floppy drives I have I've only ever run into one drive of about 8 or so that I have now that has the tantalum issue. And that one I replaced with a (modern) MLCC as recommended by one of the PCjr guys who repaired a ton of the systems when Computer Reset closed.

I don't think ESR gets worse for higher rated tantalums, they are physically much larger and have more surface area to interact with... Maybe old ones did.

Another issue is that on boards with many old tantalums (20+) the voltage on the 5v line may drop to 4.85 or lower. This is close to the minimum voltage on some parts. Replacing only the ones near the AT power connect can raise it back up to 4.9v. This happened on one of my boards. I replaced all the caps on another one of my boards and it output 4.99v.