I think that a high level doctor may have a lot of value for you:
- if you have key players that cannot be injured w/o creating huge negative impact on your team (such as in POs)
- if you train players for U21 / NT or to generate money on the transfer list.
The value of a doctor is significant as you can read here (Level 4 doctor corresponds to level 8 before the reform):
(40900.10)