I keep the 10 Token academy players too since they sell for WAY more money then you could get for 10 Tokens. For example, my last 10 T academy player was 72% ability with a $5 M market value [I'm only level 4]. Just with standard roster training (not powertraining) he'll be well over $6 M by the time I sell him at the end of the season. The current lowest offer for me for cash is $2.3 M for 15 tokens. It's (nearly) free money.
Oh, I don't know if the price of the second player increases as you level up, it's 10 tokens for me at this level (4).