I think, in the end, it will all be the same... Why? Listen carefully:
Let's say I train my players for myself, and I keep 3 of them and sell 2... I would train those 2 until they are 20, and sell them when they are marvelous... If you train your 5 players you'll sell them when they are proficient... Every year you'll have to buy 4-5 good trainees, and you know how expensive they are... You may get 1 on the draft :D And while you're spending whole lot of money on the rest of the team (let's say if you train SG/PG, you must buy SF/PF/C), I'm getting those kind of players by training... And I still can buy good players by selling those 2 every couple of years...
Cause, on the higher levels, the prices will be a lot higher... If everyone would do like you, then the market would be full of those 1-year trainees, and they would be a lot cheaper then the ones trained for more years...
For example, I bought a center with 4 respectable main Skills for 550k, and I bought other one who has 3 respectable Skills and 1 proficient, and I payed 780k... That's 230k difference, and it's just two points difference in one Skill... Now, can you imagine how big that difference will be on higher Skills? And yes, you may say I overpaid them, but that's the cheapest price I got in days...