Its impossible to make a profit in this game because you lose Tokens every time you buy. If Nordeus offered a token gain when selling a player even if it was just one than you could make a profit (If only marginal)

As for your main question I personally only ever buy level 39's that have a special ability, although i am convinced that the special ability is rubbish. A special ability even though it can cost you 250 tokens (£20) to give a player a special ability doesn't increase a players transfer value, this to me is ludicrous and all but proves that the special ability is simply a way to take tokens from players without any reward.