Hi TempleK!
Reading your post through, I find myself wondering why you are considering a sale and new purchase.
Hard to imagine a nicer bike with lower maintenance needs; what does it now lack for you? Not questioning your decision, just thinking if I knew why, I could offer more focused, helpful suggestions.
If the bike seems tired, a respray and some new components can freshen things right up again and make it feel "new". Even a change of tires can make a big difference.
If you find yourself craving a derailleur drivetrain, then the current Sherpa would be a similar bike with a different drivetrain.
Sadly, used bikes of any make don't bring as much on resale as new ones cost. The eBay sale through Thorn is surely one way to go, or if you wished to avoid commission, something like Gumtree, advertising here on the Forum, or on the CTC forum are all good ways to go.
I probably *should* sell-on some of mine that aren't ridden so much, but as a soggy sentimentalist who loves fine tools I can't bear to part with any, especially when seeing and riding them brings back many happy memories.
Best of luck whichever way you decide to go, and you're more than welcome to post it here if you decide to sell. Pictures go far in getting a good price, so the tutorial I wrote on how to easily post photos might come in handy:
http://www.thorncycles.co.uk/forums/index.php?topic=4313.0Best,
Dan.