I've had a succession of Honda NTV's over the years and been very happy with them. They are pretty bulletproof, being shaft drive, yet still a nice commuter ride.
I bumped into a previous owner of one of my NTV's who told me he'd taken it touring around Norway and Sweden, while my father had a Deauville for a year doing roving traffic reports for a local Radio station and he said it was more comfortable than his Harley for long rides.
They were quite popular in years past and were manufactured for many years, so there are plenty of old bikes for sale as runners, for spares or repair, or been broken up in scrap yards. It was also popular enough to encourage people to manufacture pattern parts for it.
The earlier NTV600's are now dirt cheap, and had the prettier short exhaust pipe, but the later NTV650's were manufactured for more years. The 650's also have more in common with modern Honda Deauville (NT700V). The NTVs, IMHO, were conceived of during the nice sweet spot in bike design, between modern techniques being perfected (they are much smoother than their predecessor, the CX500) and bikes getting unnecessarily complex (is fuel injection really necessary?).
The only real downside to the design is access to the carbs and spark plugs. The compact arrangement of the engine and chassis, which makes it such a nice shape for commuting also complicates access to some components. It's not as bad as some bikes, but might be a consideration if you intend to be stripping the cylinder heads every weekend. *8')
Finally, I managed to pick up a copy of the Honda service manual quite cheaply, which is quite useful.
Overall the NTV series benefits from a nice, reliable design and you soon get used to the foibles of shaft drive. While it feels a little odd under hard acceleration at first, compared to chain or belt driven bikes, the fact that you never have to worry about lubrication or tensioning will win you over if you are doing enough miles.