I think the 'better than +2' way is valid enough. +2 is the default, if you will, which is a sure thing if you decide to get it. If you're rerolling, it's probably because you want--maybe need--a +3 or more.
With the 38% chance at rolling better than +2 from the initial -2, it means it might be more advantageous to just take the +2 instead of risking a bad roll in the hopes of getting +3.
It comes down to whether it's worth it vs. the +2. Or worth it for the risk of a +1 or worse.