As long as the L20s are in good shape - and you like how they sound - I doubt you could find a new speaker that would perform as well at that price.
Yamaha CX-A5000 - Acurus A100x3 & Outlaw 7075 - Salk Song Towers - Custom Selah Audio Center - Oppo 103 - Marantz TT42 ***GO SEAHAWKS *** Twas a woman who drove me to drink. I never had the decency to write and thank her ~ WC Fields
I had the CSW 6 and returned it, I wasn't impressed. The cone tweeter is obsolete.
I've never heard the L20T, but I'm not sure if it's worth getting a JBL bookshelf. I had older JBLS (L166) and they were fairly colored and a bit harsh. The main attraction of classic JBLs for me is the ass-kicking power, and you won't get that with a bookshelf. I'd be inclined to go for something more modern.