It seems natural that, since the allies had more planes, crew, and ordinance than the Germans, it would make sense to simply overwhelm the defenders by wearing them down in a given area.
Not only would the defenders themselves perform poorly as they fought fatigue, the German's logistical capabilities to provide ammunition and fuel would be stretched as well. The Germans would then have to either reposition people and planes, leaving other areas vulnerable, but also furthering their logistical issues.
The potential problem that I see is that early waves would be chewed up by the AA and fighters focused on them, but perhaps that could be managed by having them bomb from higher altitudes and sending more fighter escorts on early waves.
Spreading the attack out would give the defending fighters more opportunities to make repeated attacks on smaller groups of bombers, landing and refuelling for multiple sorties. It would have been a particularly bad idea for the RAF through 1943 when German night defences were focused in the Kammhuber Line, a series of Himmelbelt zones each of which directly controlled a limited number of nightfighters; the most successful tactic was to overwhelm a single point with a concentrated stream of bombers in as short a time as possible to limit the opportunities for interception.
Both the RAF and USAAF also used massive quantities of incendiary bombs, fire being the most effective way of causing destruction when accuracy was lacking, and these were much more effective when dropped in concentrated quantities.
The RAF did fly small scale harassing raids, primarily with the Mosquitoes of the Light Night Striking Force that were far more difficult targets for night fighters, but generally concentrating resources was more effective.