If it isn't broke don't fix it...lol! Berkeley releases new versions quite often, it's best to leave them alone until the bugs are worked out. I upgrade my clients maybe once a year. There's no real point unless your current client has issues or the new client has features that you would find useful.

My advice is that if you have a 64bit operating system (or can use one for nothing) then do, and use the up to date 64bit version of Boinc, because that way you can do up to 35percent more work, depending on the projects. Thats as good as upgrading a Q6600 to a Q9450 on a 32bit system, well except it costs nothing!
More recent versions of Boinc tend to be better, remove bugs and speed up some processes and some upgrades are required to run some tasks.

Well Relheok how did you find it worked for you?
I found with my Q6600 got about a 20% boost
as best as I can tell, for going from 32 bit vista
to 64 bit win7.