I think it mostly depends on at what level of the game your at. In D.V and D.IV leagues, i dont see the investment into a high level doctor being worth it. The majority of newer teams should be developing 18-21 year olds, and should be watching their minutes really close already. I only experienced one injury amongst my 3-4 trainees at C/PF in those few years. Meanwhile, i didn't care as much for the veterans i was plugging into PG/SG/SF, and consequently lost a few games while i was training my 18-19 year olds. Now that i've gotten to D.IV and am plugging along in the creation of a bigger arena, i've invested in a better doctor to ensure that these now 20-21 year olds who are responsible for keeping me in D.IV stay healthier. I just got hit with another 2 week injury to my backup PF, but other than that i've had a pretty run with health (just one other injury to my starting SG earlier in the year when i wasn't managing as closely as i am now).
At D.IV, it's just as easy to find a veteran 11th or 12th man for 4-5k salary and less than 10k cash, so the math suggests after severance fees that it's just cheaper to go that way. This would be even more true to D.V