Love illuminated nocks! Will never go hunting without them (where legal of course). And I don't give a rip about P & Y.
As far as the added weight, I haven't noticed much difference in flight out to 40 yards or so. However, I'm a bit AR, so I epoxy short threaded rods into regular nocks so I can practice with nocks of the same weight (25 grains for Luminocks and 20 grains for Nockturnals.)