Of course it's a risk. If you tie up a 15 year old on a 6 year (Dundee Utd special) contract you end up with a squad of Dom Thomas, Craig Moore and Bob McHugh etc.. We have streamlined our acadmey this year and are focusing on developing a smaller group of better players with targeted positions.
It's all very well saying sign up half a dozen youngsters on 6 year contracts, but that is assuming all 6 will be good enough to be around for the entire 6 years. More likely half of them (or more) will be punted each year - which is the norm at most clubs - and you need to bring in another 3 or 4 on the same 6 year contracts. So over those years, you will have, conservatively, invested in over 20 players on those 6 year contracts. Suddenly not so cheap.
And that's assuming youngsters would sign up for that length of time which, given the number of agents sniffing around with their advice, is extremely unlikely.