A doctor is probably the least valuable member of your staff. Especially at your league level, it's really not worth it. Anything above a "basic" doctor will probably be around $10k/week, and common sense says that for you, a $10k/week player is much more valuable than a doctor at that same price. Also, while it sucks getting an injury, you're in a very good position with such a deep team, while an injury will hurt, you have the depth to make up for it, especially if you added another $10k player rather than a $10k doctor.
i agree a lot with this post, if the player are still rather cheap, it is more usefull to put the money directly in the roster or on the bank account to get a replacement player in case of injury then paying the "insurance" a doctor give you.
The better your player get, and the higher the slary of them become, the more useful is a doctor.