Interesting thread. Appropriate to me, since I spent time earlier this week going back to one of my courses and examining all the bunkers for removal, resizing, or renovation to get a new look, reduce maintenance, etc. (and to better challenge the Nationwide Tour players who visit each year)
Interesting points include the function of bunkers that require lengthening ability. It is starting to work on both ends of the multiple tees. Generally, I don't add bunkers for the really long hitters. Narrower fw, etc. are cheaper for the few who really hit it that long. But, lately I have really been shortening up the forward tees. If the typical woman/jr/beginner playing there is hitting it about 140 off the tee, max hole length should be 270 on a par 4. From the tees for good males hitting it close to 300, that would be the equivalent of a 500 par 4, meaning the tees would be separated by about 230 yards. If a fw bunker is place at 130 from the fw tee it would be 360 from the backs, giving it two functions - normal short hitters and the occaisional long knocker.
Even with that, it occurs to me that modern fw bunkers themselves ought to be lengthened, not unlike Pete Dye strip bunkers, to accomodate the vast distance differentials. If we want to save money, or achieve a different look, then we scatter several smaller bunkers up the the fw, rather than a solid strip. And, by staggering some closer and further from the fw, we can get some more subtle effects than a Cape like carry bunker all down the fw for everyone.
But, that is just me projecting what might last in the future.
As to existing courses, I find that bunkers get axed specifically, and not just entire schemes (although that does happen when someone decides to "freshen" the course. Bunkers that get removed are often cited as "recieving too much play" or "recieving too little play." There is no set rule for "the right amount of play" but most memberships seem to know it when they see it......TD's idea of placing them at different distances is fine, although it they were extreme - say 100 yards and 400 yards off the tee, they probably have less chance of lasting.