I think the more penal the bunker, the more the golfer will attempt to avoid it.
A mildly penal bunker might cause the golfer to flirt it without being too concerned with the consequences of going in it.
However, a deep bunker would make the golfer think again about taking the aggressive line.
On the other hand, the recovery shot is perhaps the greatest part of the game.
Making all the bunkers unrecoverable removes the recovery aspect and becomes a total strategic nightmare where bunkers are just as bad as water, sometimes better in that you can advance your ball a little, sometimes worse when you end up not clearing the lip and having to hit again (and again and again).
I think the best designs should have some absolutely penal bunkers, where you have to basically flop to get out. Think pot bunkers in UK.
These should especially be on short par 4s and 5s where the golfer is taking on major risk by attempting to pull a shot off that could be very rewarding.
However, on a mid-long par 4, I think the lips should be penal, but not enough to discourage the daring golfer to pull out a 7-iron and try to get to the green. Of course, no tough bunker is ever going to allow one to hit a 6-iron or less (lip is too low). IMO, the lip should tempt the daring to take it on, so to say, but still have that risk reward aspect. Hit it absolutely perfect, and have a shot at getting to the green. Fail, and have to hit the shot again, and most likely be closer to the lip. The safe golfer can easily take his medicine and pitch out.
The deep, penal bunker makes the game one-dimensional, and the second shot automatic. The bunkers I am describing are penal enough to cause damage to your score, but not penal enough as to tempt the daring golfer who took the aggressive line in the first place to try and pull off a tough recovery.