I appreciate the variety of thoughts and comments on this thread. A lot of good stuff here. My not-so-firm conclusions:
Yes, a course can be great even if takes 5+ hours ordinarily to complete the round. It is often those things we like about gca that has an impact of the pace of play: the routing over considerable elevation changes and around environmentally sensitive areas; rolling terrain that creates difficult lies and feeds the ball into hazards and obstacles; large green complexes with lot of slope, internal contouring, run-away and false slopes; large bunkers which while aesthetically pleasing are hard to maintain and even more difficult for the average golfer to get the ball back into play; flanking penalty areas and native vegetation close to lines of play; blindness; large scale, etc. For some of us who like to play fast, we sometimes have to consider whether the features we love more than offset being able to play in our definition of what is reasonable. I do wonder if one of the reasons we like so many of the classical golf courses is because they tend to be simpler, cleaner; no attempt seems to have been made to create 18 signature holes.
No, I don't think it is a good idea to create or publicize a goal of 5 hours. As a sometime referee and tournament helper, I find the practice of setting highly generous time standards- say 4:45 for a three ball in 10-minute starting times- ensures slow play. My preference would be to set aggressive targets as they did at TOC (4 hours) and manage the pace of play accordingly. The old rule book's etiquette section stated that if a group behind is playing faster, let them through, and certainly if there is a hole or more open in front. I understand that conflict is not a good thing, but to appease a slow group just creates conflict for the folks behind (we had a case in Carrollton, TX where a golfer hit into another group after waiting most of the round, a fight ensued, and the instigator busted the skull of a guy in the offending group with a club, putting the guy in the hospital with permanent damage).
Yes, I think architects and superintendents have a strong professional obligation to doing the type of things that further the interests of the game. Pace of play is cited as a big factor in the lower participation rates. Sacrificing aesthetics a bit (e.g. putting eye brows on bunkers at a daily fee course; forcing a long climb to a high tee box for a view with no effect on the playability of the hole; being different/"out of the box" for the sake of it/brand differentiation) for better efficiency is fine with me. Superintendents could pay much more attention to how they set up the course for the day's play and weather condition- the responsibility for setting tees and hole locations should fall to workers who understand the game well and aren't too zonked out early in the morning to do a proper job.
The owner's objectives and those of the clients are, of course, highly important. Playing Pebble Beach in under 4 hours is not a good goal though I've done it once and thoroughly enjoyed it. Judging from the full tee sheets at $$$$$ rates, it appears that the 5+ hour round is desirable at any number of golf resorts (I remember a 6-hour round at Barona Creek during the first King Putter). As a golfer who is clearly concerned with spending too much time on the course, I just won't be visiting these type of places very often. But, I am the type of golfer who doesn't find caddies yelling across fairways to their buddies and making loud Tarzan calls that can be heard several holes away part of a pleasant experience. I do think that caddies slow things way down, but it is not because they want to spend an extra hour on the course. It is likely that they perceive their role to be part of the experience. If the client wants a Spieth/Greller experience and it has a bearing on the "tip" (mandatory minimum of $X + more for good service), they're going to provide it. When pointing fingers, remember where 3 are pointing to.