It depends how precise you're trying to dial things in and what you're growing. For most folks, I'd say it's not worth the upgrade, especially if you're not growing SPS and have a small tank. The key features of the HD vs regular are being able to borrow intensity from other channels, so you can actually replicate the Coral AB+ spectrum. You'll also get some additional PAR.
I'm actually having the same debate myself and am leaning towards upgrading because I'm looking for as much PAR and the best spectrum I can get for the acros near the top of my tank, without completely frying the lower light corals that sit 12 inches down on the sand. I've been going back and forth between keeping the regular Prime or upgrading to a Prime HD or Radion X15.
