The Gunboat 62, Looking for Elvis, definitely does/did some serious cruising. I've seen it a number of times in the Caribbean.
The couple in this article doesn't sound like they are sitting in a marina or hiring a crew to get them anywhere, either:
There was an article in one of the US sailing magazines within the last year or two of a Gunboat division in the Heineken Regatta, as well.
I agree with you on the point of the cost of a Gunboat. Some owners may even have purchased a Gunboat to charter out to help pay for them, but want a high performance "play thing" at their disposal and hire a crew to do so. However, from what I have read (in magazines like above) I get the impression that while most Gunboat owners do have a certain degree of wealth (and may have purchased them through their corporations, or created one to purchase it), they are serious sailors and use the boat to do some serious sailing.
I know if I could ever own one, I would!