You would be putting a somewhat sensitive electrical device out in the open, so expect the life span to drop as they are exposed to dirt, water, salt, etc. that the race guys do not deal with on a track.
As far as more power, I don't think it would make a difference. To replace the charge used up during idling, the alternator would be more heavily loaded during driving. You think the lights dimming at idle are bad now, take the alternator completely out of the circuit and watch things get dim. Plus, you aren't really eliminating the charging load. All you are doing is moving that load from the engine to the driveline. The drag is still there. An easier change would be to add a toggle switch to disconnect the field of the alternator when you running in the upper rpm range. That is still only worth a few horses at best.
