Dave, if the spring rate is wrong it's a bad base for the rest of the settings. The emulators I got were £80, compared to the cartride kits around for £600. The emulators are adjustable (just a pain to get out each time) and are nowhere near as good at cartridge in terms of adjustment, but still miles better than stock. I thought at that price it is not a big gamble to try them and they work for me.
As svenrico says, get servicable shocks. I rate my Bitubo and mid range were £380. The rebound and compression are adjusted together with a slider from 1 - 5. It's enough to get a decent set up unless you are going to the track. I spoke with MCT Suspension and Steve Jordan's who both suggested Nitrons over Hagon, or the KTECH Razor. But they were another 2 or 3 hundred more than the Bitubo and they are going on a Bonneville after all
I found Bike Revival had a lot of options and good to talk to about options you might not have considered
http://www.bikerevival.com/page1.html