JUCOs have some inherent problems - and some inherent benefits.
The Pluses:
1. More physically mature. Physically, you're getting a product that is close to finished - or at least it's clearer what potential for growth they have compared to a 17 or 18-year old.
2. Have gotten over the "away from home" syndrome most kids go through.
3. Have - presumably - played in a system that is a bit closer to college.
4. Have - again, presumably - played against better competition and have a little better idea of the speed of the college game.
5. Have been through a few hard knocks - hence being in JC in the first place - and might be a little more appreciative of the chance at a D-1 slot. They might also be a bit more able to handle adversity.
The Minuses:
1. There's a reason most of them are in JC to begin with...
2. They may have the "instant stardom" syndrome; i.e., they have a limited time left to "make it to the next level" and therefore may be a bit more resistent to changing positions, techniques, etc.
3. Have a limited time in which to contribute.
4. Generally need some time to become acclimated to the college game - rare is the JC that can actually come in and immediately contribute.
5. Limited loyalty - someone that is going to be in the system for only a couple of years as opposed to 4 or 5 years may not have the same degree of loyalty to the program.
Of course, all of this depends on the individual player. As a rule, JUCOs are "quick-fix" guys. There are a few exceptions where the kid is a stud that was simply a bit too lazy with the books, but only a few. For the most part, you look for a JC kid to come in and plug a hole - not necessarily be the star at a position (although that is certainly possible). They provide depth and someone that should be able to contribute more quickly than a high school player.
But I can't think of any team that has had sustained, overwhelming sucess by relying on JUCOs. For that, you must use high school players that will be in the program longer.
In other words, once the foundation is in place, the bulk of each class has to be high school players, with the occasional stud JC kid for good measure.
I suspect that as time goes on, and as depth is re-established in the program, you'll see fewer and fewer JUCOs in the program. I hope so, anyway...