Well, then it's basically a one season boost. In this case what is the point to hide the extra boost? No one would ever see it except you. Also if a player with boost will be sold will he keep the boost with the new team or not? If yes it should be marked as it raises the player's worth. If not, again, what is the point to hide it?
I like the idea of the TC but I would rather give boost for a higher price, like 100k-200k-300k-600k-1M (or even higher), the raise should be something similar to draft points system. The higher price is essential, as the boost won't raise salary. Let's see your example, I have a center with 16 rebound, near to pop to 17. I will pay 100k for a 5-day training camp and I'll have a center with 18 rebound for a whole season (22 league games, 4-10 cup games and the whole PO)! If I train my center to 18 rebounds it would mean (at least) a 60k salary raise/week which is (again, at least) 840k/season.
Also I don't really get this:
1. The effect of the training
1 day training effect = the effect of 1 week full 2 positions training
2 days training effect = the effect of 1 week full 2 positions training
They have the same effect, I guess you meant 2 weeks of training for the 2-day training camp.
One more question: Training camp is available for only one player or you can buy multiple training camps for different players? If it is for multiple players, imagine what would happen in the first divisions with full of NT-caliber players and a lot of cash...
I suggest you to work a bit more on the idea as it is really good but you didn't count the effects and the reasonable prices for that and lots of other details are not clear (for example will the age counts in TC effect as it counts for "normal" training or the mentioned case with selling the player).