The way our charging system works, the lower wattage is an advantage only to a point since the alternator is producing 100% of it's capacity all the time regardless of the load.
Taking a stock bike with no plans for any additional lighting or accessory loads and changing to LED's will gain nothing with regards to the longevity of the charging system. Going over every connector and cleaning or replacing will keep the system running healthy longer.
Now if that LED headlight is brighter and shines farther than an HID then I think it would be worth the price for safety, well not the regular price of $800+.