I have consulted with a few supers recently who went with BBB to reduce the sand wash on faces. Both said they saved $70-80K per year in unscheduled shoveling after rains. I would have guessed $15-20.
If you count all the work (including new white sand, I find the total cost of bunker renovation to be about $6 per SF.
Either way, assuming 3.5% interest rates, and about $70 per thousand annually, it would seem, based on those numbers, that any BBB investment up to $1,000,000 (or over 166,000 bunker SF, when most courses have 50-125K sf of bunkers) would pay off just in labor savings.
As to the architect and contractor trying to keep busy, well, I have never demanded any course install that. I usually use the old CBM quote about bringing the cavalry in for the day to "prepare" the bunkers suitably for play. It has never been taken up. However, the decision usually comes from the clubs or courses themselves, if that tells you anything about Tom's somewhat snarky comment!
It is pretty competitive, so I doubt the contractors make big bank on the smaller $$ projects. As an architect, I don't find I can charge a lot for it, or even get called, unless they use that opportunity to reduce or redesign the bunkers.
BTW, if you are deciding to add bunker liners, it does pay to use that opportunity to rethink your bunkers, both in total number and size, the ones that have "crept away" from the greens (or vice versa) As mentioned, it can also make sense to change design a bit to max out the benefits. If there are bunkers that don't see a lot of "action" perhaps they could be removed similar to Tillie's thoughts on duffer headaches.
In cloth liners in particular, you will probably be hand raking, so reducing some of the bunker size, and perhaps widening out any noses to ease mowing is a good way to go.