Gwauk -
Go and really listen to the speakers he wants to trade. Decide for yourself that way. The Quartets are fantastic speakers. My Dad has a pair and we're trying to decide what to do with them because he wants to run a 5.1 system and is having difficulty finding speakers to match in the rear and center. We're trying to avoid replacing them as much as we can because he likes them so much.
Just because someone says their speakers are equivalent to such-and-such doesn't mean that they are. Ask him exactly what model they are and then query
RBH to get their view on what a comparable model in today's world would be. They'll be the expert on this. I would assume that the individual who wants to trade sees some sort of advantage in the straight up trade or they wouldn't be willing to do it.
Watch ebay, audiogon.com and craigslist to see what people are selling them for(I've been seeing asking prices of ~$400.00). Then check out what the other speakers are going for. If they're not equivalent in monetary value or the Klipsch sell for more, then it isn't a good deal in my view. Don't sell yourself short. I'm not a huge Klipsch listener or enthusiast, but the Quartets have always sounded great. Huge speakers, very efficient, and very neutral.
-pat