IMO, they are worth the money if only for smoother operation.
HP increase due to addition of roller rockers is something only a Dyno is going to pick up. You won't feel it in the seat of your pants.
The problem is, you can spend a tone of $$$ on them, so knowing when enough is enough is the trick. Comp Cams offers their line of Magnum Roller Rockers, which are a stock style "Steel" rocker with roller bearing tip that are fairly reasonably priced, but I've seen several VMF posts complaining of rocker noise when using them.
I'm running Crane Roller Rockers, which are cast aluminum with needle bearing pivots and roller tips (Similar to Comp Cams Pro-Magnum). IIRC, they cost me around $200.00, which was closer to the Comp Magnums. I have found them to be very quiet and have had no problems with them to date.
I also don't think there's any need to go with the billet aluminum, or machined aluminum race rockers for the type of building most of us are doing.
I've got the comp cams roller rockers, and they are a bit noisy, but nothing that can't be lived with. I would go ahead and do the roller rockers, as most of the sets are not that expensive, and if you have to buy new rockers anyway??, then it would not be worth it to spend money on regular ones.