There's always the option to sell them or train their secondaries first before they have become too big a fish in a small pond. Star potential is too low for bigs and perhaps barely acceptable for guards IMO.
If you're going to sell the guys when they cap, does it matter if that cap is star or superstar, in the grand scheme of things? The lower potential just means that you're starting your next training that much earlier, at which point you get trainees at a potential level based on where you want to be in some four or five seasons from then. I find it ridiculous to suggest that a team starting out in V needs to be training guys that would be its go-to players if they ever make it up to I in some 10-15 seasons time, especially given the stark reality of how few teams progress to that level.
As far as star potential being too low, again it depends on what level you're talking about. But it's certainly high enough to get a team from V to III, at least in the USA, and to maintain a spot in III while starting the next set of training -- and any argument against that is simply refuted by: "If you were right, I would be demoting." No argument that something can't be done can hold up against an example where it has been done.
The point is, and this is where i fear you are confusing new owners in this game...is that Star potential caps very quick....and often when you are new, you find a player or two you get excited about, envision that player being with your team forever, and that you will train him up, and he will help promote over and over and over....but then, after a couple of a seasons, boom, he's capped. That's dissapointing. Again, if you have a short term plan for a guy, fine, then that's your plan. but the notion that Star potential players are great players to train as the foundation of your team? Seriously? That just doesn't make a lot of sense.
If you plan to build a team, and grow your team, and advance through the ranks, one of the best ways to do that is to have trainees that have higher potential that you can continue to train, but at the same time rely on contributors to your victories. Its a great thing to being playing a guy who has a salary of 26K, however, his new training pops has his projected salary much higher. That's great value under the "play now, pay later" program.
One of the biggest gripes you hear about teams in higher divisions is that its too difficult to train players, and win. Who can take an 18 year old 5K player and stick him in the starting lineup with his 50K to 100K players and not have it affect the team? So training Star, to see him cap shortly, and then start over again, becomes more unrreleastic the higher you go ion the game. Now, if you are planning to stay in DIII, then I guess you can try to make that work.
Newer Owners: Just make sure you have a plan. The best thing to do is to go the Mentors thread in these helps forums, and find someone who will work with you one on one with your team. Training is a huge part of BuzzerBeater and can be the difference between quickly rising through the ranks, and being stuck in mediocrity. Training players, and managing of minutes that is required is crucial, so make sure you understand that fully as you set your long term goals/plans in BuzzerBeater.