It sounds good to me Stefan - you could even increase the negative values by one in each category (from -1 to -2 for example) and it would still be balanced, because the scenario creator would take this into account with his scenario victory conditions.
And let's not forget, that even in large scenarios, these medical units would be fairly rare, so their share of the overall points gained or lost would be small.
Also the negative point value is to discourage blind shelling and being deliberately targeted, but it should be large enough of a negative value that it will *actively* discourage that kind of bad behavior (Geneva Conventions and all).
And again, thanks to all of you guys for helping with this!