I purchased the KG 5.5's (KG was the next series down from the KLF) new in '93 ($700)
and added the C7 in '98 ($275)
. It was a very fun system that I ended up selling to a good buddy (along with SS-1 surrounds and a SW-15 II sub) in '03 when I decided I wanted to broaden my speaker horizons ($500 for the 5.5's and $250 for the C7...both mint)
. My buddy then decided to sell them in '10 when he made a move to in-walls. I strongly resisted the urge to buy them back (as I needed more speakers like I needed more holes in my head); he sold them to a friend of his for what he gave me in '03.
If they are in nice shape, Klipsch (or any quality brand really) speakers will bottom out and then carry a consistent value through the years. Checking eBay, there's only been one pair sold in the last 10 weeks and they went for $404 at the end of May. There is a pair currently listed for $650. I would say $600 is in the right ballpark if they are nice...
I believe the the 'rattles' come from the the mdf panel's joints loosening up. Repair can be quite problematic if the speaker still has a nice finish on it...