Very nice bike. Set up much like mine (before I started modifying mine):

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I'd do it in stages. I would get a bigger cog, 20T to 22, and a new chain, and try that first. Then I would go with Sun CR-18 rims. If you want to cheat you can just tape the new rim to the old and transfer the spokes over, assuming you have Raleigh Pattern rims.

That's all I've done so far, but I just got an S5 hub, and I'm going to service it and install that next. You can get an Aluminum stem and bars, too, for not that much more, but I don't know how much weight it will save you.