Are you talking about an old VW Beetle, a classic car, or are you talking about buying one of the newer Beetles currently on the market?
If you’re talking about a classic Beetle I think you probably wouldn’t like driving one in modern traffic. The classic Beetle is ancient technology compared to anything you’re used to driving. An old Beetle makes a nice hobby car to drive occasionally, but I wouldn’t want to use one as daily transportation, especially on the freeway around DC.
If you’re talking about the current Beetle, I don’t see any reason you wouldn’t like one if that’s what you want. The New Beetle has very large door openings and lots of room inside (in the front seat, at least). A friend of mine who is quite large in all dimensions really likes his New Beetle because it’s easy for him to get in and out of.
There are some reliability issues with late-model Beetles, and VWs in general, so your mechanic may be correct there. As far as NH winters go, I’m sure there are New Beetles in NH, and with good winter tires it should be fine. A New Beetle will go anywhere any other front wheel drive car will go.
Either way, classic or new, I suggest you test drive a Beetle Convertible and see what you think. You can take advice and suggestions from anyone you like, but you really should test drive a Beetle and see if it’s really what you want before you decide.