I am a little afraid of some boosters because of the problems you could get if you overdo it.
I DESTROYED my plants with Gravity because I had temperature problems whil I was using it. It is a pretty amazing product if you have TOTAL control over your environment. It is said to add around another 20% to your weight, but you have to use it carefully.
Bud organic bud boosters like bone meal are nice- bone meal mixed in with the soil at the last transplant.
I have heard VERY good things about the 'PK' bud booster. It isn;'t something I have experience with.
If you are using Sweet, you can still add molasses to add more carbon- the Sweet has carb synthesizers and if you give it another sugar source, it will helps the plant use it better. Bonus, you can feed molasses right to the end. My friend says he has been able to actually TASTE the molasses in the finished product, but not in a bad way.
Just some thoughts anyway!