Thanks everybody for the welcomes and suggestions!
First off, I have pictures. (I tried to crop pictures and reduce picture sizes, so as not to bog down browsers. Hopefully I struck a good balance between detail and bandwidth)
The bright spot:
Based on suggestions from this forum, I bought a file and (gulp) filed down the lump on the quill. I smoothed up some of the worst scratches with 220 grit sandpaper. I rewaxed the quill, and this time also waxed inside the hole (trying not to leave a lot of residue to pick up sawdust). I checked the groove for burrs and found a little bit of a lump near the bright spot (on the side of the groove) so I filed that a little too. I held off on increasing the spring tension, wanting to see what difference these changes would make first.
This is what the quill looked like after I was done:
I do have a couple of questions. First off, in the above pictures you can see a rubber gasket around the quill. This started off being stuck to the headstock, but came loose the first time I tried to clean out the pinion with the big wire brush (I had to jam the brush in pretty hard to get the bristles through the hole, because it was a bit oversized, and when I pulled it out again the gasket came with it.) I put the gasket back between the headstock and the snap-ring on the quill but now it moves with the quill instead of staying with the headstock. Is this a problem, and if so, what should I do?
Second, there is a rubber ring (another gasket?) around one of the waytubes. I don't see any gaps it might fit into. Is it something I should worry about, and if so, what should I do about it?
The rubber ring:
And last off, my major claim to woodworking fame is that I build a canoe a few summers ago--a feat I hope to duplicate again soon. As I look through the Woodworking for Everyone book I realize that the woodworking required to build a canoe is really pretty basic, but it's my most impressive project to date, so here it is:
Me and my canoe in Quetico Provincial Park:
The quill extends and retracts much more smoothly now. It isn't quite perfect, but 97% of the problem is gone and I am much happier.