Mathematically, if you have 4 seconds before Demolish is about to expire and you're about to reapply it, Meditation may be a net potency gain (it takes half the time of another GCD for 50 potency [1/5 of 250] + 50 potency from extra Demolish tick, for 100 potency over half a GCD, which is higher than MNK average from weaponskills). However, that potency gain would heavily depend on skill speed - you need to guarantee an extra tick from Demolish for it to be a gain. Otherwise, it's 50 potency over half a GCD, which is less than average. Doing standard rotation (using two Snap Punches between each Demolish) at GL3 at 1000-ish skill speed I'm only seeing 1-2 seconds left on the timer for me.

I may be wrong on this, but as a rule of thumb, I'd say that overall it's not worth it.