I agree with tuddu, Primary skills are a "must" for u-21 players. Users aren't too much in Norway, so probably a talented players can't be substituted by another one, and you don't need to waste this pool of talent.
A great U-21 hasn't so low potential players. For Example, under "all star" level it's very difficult to found someone in the biggest and strongest u-21 teams and more you can develop your player in primary skills, more he will become important. It's like 100m. First one who arrives win, and you've 4 seasons to arrive.
Training outside position when salary is high it's a problem for everyone, but sometimes it depends on what you need and what you like to have with that player. For Example a well trained big-man after U-21 needs only 1vs1 SF-PF training except primary skills, to increase his value ingame. If you like to have a PF, you will train OD/Passing, but's your decision. Vice Versa for PG.
This kind of thinking can be done in a country with not so much users, like Norway. In other countries competition and big "talent pool" will give to their coaches different and stronger and useful players for every situation,so you may have a internal SF, a perimetral PF, a Passing PG, a defending SG and so on...