Thanks for your comments! It's always good to hear about people trying out autonomous mode :)
It should be possible to assign values to enums, and when I typed in the enum in your post it worked correctly (MSG_REQUEST_ESCORT was 500, etc.). Are you using the latest version (v1.3)? I don't remember there being a problem with enums in the earlier versions but it's possible that there was and I fixed it.
The game does use look-up tables for trig functions, although they're not as efficient as they could be. But the in-game instruction cost of calling these functions is just an arbitrary number; it doesn't map directly on to the performance cost of the game itself doing the calculations and I think if it was more accurate the trig functions would probably be much more expensive (especially atan2, which is quite complicated).
I agree that custom games could be improved - the problem, as always, is time! I'd like to get to it eventually, though.