The relative weakness of gravity (it should be stronger to make the numbers work) intrigues me.
Some iterations of string theory (for what that is worth) postulates that gravity IS strong, but the effect bleeding off elsewhere.
If true (and observable in some meaningful way), I would be hopeful that the relative stregth and weakness could be increased or decreased.
Not so much "anti-gravity" as "no gravity," making lift a much easier business.
I believe the theory is that gravity bleeds across dimensional lines so we're only seeing the narrow slice that appears within our own dimension. If this is true, there should also be random gravity wells peppering our own universe where galaxies, stars, and planets in other dimensions have masses too. It'll be an interesting development if we ever figure out a way to "see" gravity wells and confirm this.
Of course, if that theory is correct we may never be able to build antigrav equipment. Doing so would require us to widen or thin the separation between the dimensions, which could destroy the universe (or make a big hole in it where our planet is) if an accident occurred.