RE: Upgrading from a Knight Disc to Disc Elite
I'm not sure how much benefit there is. With the new disc the bolt pulls back and pulls the disc off the breechplug. I can see more sense in upgrading the old plungers from #11 and musket cap to the Extreme ignition. I did that with my Hawkeye pistol.
If you've not had any problems then you should probably just keep it as is.