Nice post. Couldn't agree more on what you say about potential for starting teams. If you are starting, you can very well pick some cheap allstars or eternal allstars to train, it will take at least 3-4 seasons for them to fulfill their potential and that's pretty much the time you need to have a decent arena, a decent fan base and start making money and being competitive. Then after those 3-4 seasons you sell your trainees, maybe keep one of them on your roster, and with the profit try to upgrade the level of your trainees. Or you can sell one of the trainees before they cap and keep training the others while buying a new one, than you will always have better trainees that could have a starting hole and others that fit as reserves/backups.
Anyway, MVP potential and above are more useful if you intend to grow national team players. After a certain threshold, salaries get too high and thus selling prices go down as well, so if you want to make a profit you shouldn't spend a lot on a trainee with high potential, training him until he caps and try to sell him. Only a very tiny percentage of teams can afford players with 100k+ wages on their rosters, so there won't be many potential costumers for your product. Not to mention that if you are training a player with a 100k salary he will cost you 1,4kk/season only to keep him. OK, your team will be competitive with him on your roster, but you must take those stuff into account when deciding who to train.