I don't know what you consider a worthwhile improvement, but I will tell you how it changed my sound the first time I hooked up an amp. First thing I noticed was the bass was more tight and had a bit more slam. The overall presentation was more open and clear, or for a better term, separated (especially at louder volumes). Was it night and day to me? No, not necessarily, but was it worth the money to upgrade? Absolutely. So it all depends what level of improvement you are expecting. If you are looking for the holy grail of audio solutions you won't find it by only adding an amp. If your expectations are within reason I believe you will be pleased with the performance an external amp will give you.
[This message has been edited by Jed M (edited June 21, 2003).]