Since I saw the article on speypages (sorry, on a slow connection and I can't find the link), I've had good success welding polyurethane coated lines (not so much with the PVC). With the thicker spey lines I use a smaller diameter PU coated line and melt it all together to form the loop - for the running line end I double the line up, and add a third length in the shrink tube.
For my nymphing setup I have a midspey line on the Deer Creek - it's a bit heavy and probably not as sensitive as I need, but works well when you need to get a three nymph rig out. I bought a scandi head for it, but I've only had a couple hours to cast it, and I'm thinking I need to cut it down a tad (or get better at casting it).