I'd advise you to focus on improving other areas of your ground first.

From personal experience I don't find having youth players come through to be that great. The ones you have to pay tokens for are over priced compared to better star quality players available on the market and the lower star player is only good for signing and reselling for money - which becomes a bit of a redundant commodity after a while.

It doesn't matter how quickly you improve the youth academy either, the quality of star is determined by your level, not by how good the facilities are, so I would suggest only upgrading them when you have to and focus on other areas first.