Fostex Drivers.... need some advice here..

I have a pair of Odeon Rigoletto speakers. They have two drivers in each speaker..... Audax horn tweeters and Fostex FE164 full range drivers. I want to upgrade without buying new speakers. Was looking at the FE167E drivers as replacements for the 164s. Will cost me about $120 for the new drivers. Will the difference in sound be enough to justify the cost? Any advice would be greatly appreciated!