A buddy of mine has a Dan Wesson 357 revolver with the extra barrels that he is possibly wanting to sell. It has little blue left and it is having a problem with light primer strikes. If I pull the hammer back manually and let it fall while holding the trigger it fires, but when just pulling the trigger it doesn't seem like the hammer is going all the way back and it has light primer strikes. Also, it will not lock the hammer back for SA and I thought these were SA/DA revolvers. I'm not a revolver afficiando and know very little about these pistols. I would guess that a spring kit would likely solve the firing problem. What would the value even be? He doesn't have the original box or anything. Would it even be worth reblueing?

Mint condition in the factory box with all 4 barrels, tools, and owners manual around $1800. For what you described in the condition that it is in $250 tops if that. Needs to go back to DW and have them make it right. Re-bluing around $300 give or take.

yeah, its only 3 barrels, no box, tools, or manual.

I saw a very good condition DW with only the 4" barrel at a pawn shop for $350. I was really surprised because this pawn shop sells beat up S&W and Colts for $500-$700.
I went home and checked around the gun auction sites and I was surprised the $350 price about average for this gun. Now I wish I had bought it but oh well.
With the problems you say the gun has I would pass on it.

I'm thinking if it won't lock the hammer back it's more than just springs. Not sure about "the hammer not going all the way back" in DA. The Dan Wesson has less hammer travel in DA than your typical Smith & Wesson. If it has a broken hammer sear you'll need a new hammer. That's not going to be easy and cheap.

If the extra barrels are in good shape they could be sold. But what you have here is a gun that will require a good bit of investment in repair and refinish. Then you will have a non-collectible shooter that will be worth less than you have in it. I have learned the hard way to stay away from these, unless you just love it, can't get it anywhere else, and are going to just keep it forever.

Update:
I picked up the DW for a good price. It's a Model 14-2. The grip screw was the reason for it not locking back in single action. Now it locks back. I haven't been to the range yet to check the light primer strike but I suspect it is resolved now. Problem is now the grip is loose. Guess I'll have to modify the screw or get a washer that will fit. The grips fit really poorly to the frame. I don't know what would cause that.