I’ve seen the word in older stories, specifically P.G. Wodehouse, and it seems to be some sort of bus. On Visitors’ Day at Blandings Castle, folks came from far and wide in ‘charabancs’ to tour the Castle.
But what kind of bus is it? Do you still use the term today?
It was a bus - from the French, char à bancs. http://dictionary.reference.com/search?q=charabancs
It basically is any bus that carries many passengers. Early usage, IIRC, was applied to an “open-topped” bus. This seems to back me up. 
Oh, and no, it’s obsolete.
“Charabanc” was a term in use in New Zealand up to the mid 1920s. Here, not necessarily “open topped”, but “open-sided” or toast-racked.
So in contemporary usage, should I imagine a fairly comfortable, well appointed bus, such as the kind used to ferry tourists around?
Yes, I guess the open-topped bus tours of London are the closest modern equivalent. However, obviously, motor vehicles aren’t the preserve of the wealthy that they were a century ago. A Google image search gives plenty more photographs.