for most usecases its only slightly better than using recycle.
That in lies the problem I suppose. A lot of the functionality here overlaps with recycling.
Honestly it feels like increasing the game complexity for edge cases.
I'd argue it's not really adding complication to the end user's code. The (undefined) default would still boost the creep's parts for its entire lifespan. The new variable on boosted parts likely wouldn't affect anyone adversely, and I think it unlikely many even use the existing boost variables on the individual creep parts. This is just an idea to give us more flexibility for creativity, especially since the devs are actively trying to increase the costs of boosts. Perhaps when power creeps come out (hahahahahahha) then this idea will offer greater usability since they have the potential to legitimize many more niches for creeps.