OK, putting money into the arena is probably the better long term plan although it's kinda make it tougher for you to build a team right now. I would absolutely not switch your training yet. Average starters in IV (my IV at least) are between 8-12k but really good ones range from 15k up. Check out the backcourt combo of this team from my league:
http://www.buzzerbeater.com/player/8420537/overview.aspx
http://www.buzzerbeater.com/player/8420522/overview.aspx
... And he didn't even finish first in our half of the league! Now admittedly the rest of his team sucks and he didnt manage them very well but those are the types of players you can run up against.
Having young players doesnt help you unless you're training them so what I'd do is continue training guards for at least one more full season then sell most of your younger big guys who won't be training and buy cheaper but better players in the 27-28 year old range. They're less expensive and they will help you get your foot in the door and by the time their skills start going down 3-4 seasons later you will have more money to be able to buy new players.