Someone on the EE will buy your Shockwave grip, 100%.
Although this is nothing new, a 590 14" w/Shockwave grip (you can do this yourself from parts kits & Raptor Grip purchase), I'd pick up another depending on the landed price. If reasonable, for sure I'd pick one up. Mossberg shotguns are pretty awesome, the 590A1 being the top dog.
If you don't like the raptor grip, you can always bolt up any Mossberg 500/590 wood/polymer buttstock. Even the 500 Field (short action bars) Wood forend will fit the 14". Ask me how I know...
Here's the 500 Field I transformed into a 14" using the kit I bought from SFRC, keeping the wood stocks.