A correctly tuned and connected vacuum advance should not even affect idle on a Ford as it should be connected to the delayed vacuum port on the carb. ("ported vacuum")
As for part throttle response, it could go either way....depends on your curve. Too much vacuum advance and you are pinging....
Fuel economy, perhaps, but I was always under the impression that the vacuum advance was used for cleaner emissions, although fuel economy could benefit slightly at steady state cruise speeds. (Not likely where Ben lives!
)With my old engine and the new one, I had/have a rock smooth idle, the best throttle response I've ever had in a car, and unfortunately, not enuf miles to figure out fuel economy yet....
As with all things Mangusta, your mileage may vary....!
If you are running the stock Ford distributor, follow what Ford recommends... If you are running an MSD distributor, I refuse to help you as MSD in my book stands for 'My Stupid Distributor'..... No need for flames...it's my opinion. I'm just saying that I rarely if ever hear the expression "my points or DuraSpark ignition system isn't working right".....yet I go to a Pantera club tech session and almost always hear of someone with MSD problems of one sort or another. I've been running DuraSpark II in all of my cars for over 25 years and have only had one pickup module go bad....they work, and parts are easy to come by. Difficult to argue with that sort of track record....not to mention a bazillion station wagons and trucks....
Steve