I bought the boxed 6.0 upgrade from 5.2 and Sampler.
I think it depends on what exactly you use Live for if you will notice big differences. I myself have not yet used a lot of the features yet, so I can't give you a complete overview, but some things I noticed so far are:
New mp3 codecs support: With Live 5.2 i previously had a lot of mp3s that did not open in the program cause it could not decode it. I had to convert those tracks to wav manually to use them. Now with Live 6.0 all those mp3s load with no problems.
Finding missing tracks: With Live 5.2 you had to search for all missing tracks in a project yourself. Live 6.0 has a smart feature that can figure out where tracks might be after you show it the location of one of the missing tracks. For example if you have a folder C:/Music with all your music, and you moved it's location to F:/Data/Music, Live can automatically replace your missing tracks after you replaced one yourself. This proved very useful for me; I was working on a set with already over 50+ tracks in it while I moved my music collection.
The Essential Instrument Collection: that comes with the boxed version of Live 6.0 provides you with several gigabytes of high-quality sounds from pianos, guitars, brass, woodwinds, choirs, etc. Very nice if you produce your own tracks!
New Deep Freeze: The new Deep Freeze option now allows you to still re-arrange or loop your frozen tracks. This Freeze option is used when you are working on CPU-intensive projects and allows you to temporarily save the contents of MIDI-channels to wav while you don't have to change any of the sounds in there. Freezing tracks can seriously reduce the use of the CPU.
I advise you to take a close look at all the preview videos on the Live 6 site and see if there is anything new that could be of use to you. If you can't find much, then I would advise you to keep using Live 5.2 for a while, which is still a great program
