Kawasaki Forums - Rebuild/replace Rear Shocks on a 1999 ZRX1100?

I have a 1999 ZRX1100 that I've owned for 5 years. She's my daily rider and over the last few months I can feel the bumps more and more, the front shocks have been redone recently, and im pretty sure its the rear shocks as she feels like she's bottoming out.

I've made a few adjustments to strengthen the rebound damping from 2 to 3, but that doesn't help much on the bigger potholes in the city. So I'm thinking it may be time to replace/rebuild. My question:

1. should i look to simply replace the springs? - the zrx1100 rear shocks have a nitrogen canister
2. or should i be replacing the entire shock as a unit with OEM/after market shocks?

Thank you for the help.