upgrading: 5.2.1 to 5.3 OR a new 5.3?

Hello. What is your general opinion on upgrading FreeBSD installations?
I ask this since 5.3 is close and I'm gonna move to a new hd, but I 
don't know whether is more wise to move my existing beloved 5.2.1 
install or to start anew.
Reinstalling has it pros like deleting all the possible junk. But being 
FreeBSD a very polished filesystem furnished OS, I think it might be 
safe to convert my 5.2.1 to 5.3 without inheriting too much junk.
Are there any cons? Maybe the new tecnhology may leave unexpected 
problems pending against the old one?
I must say I'm really in favour of a new install, but thinking to the 
many customizations and mods I've done and to the time it could take to 
redo them...
Obviously i would take my conf. files with me, upgrading them when 
necessary.
Opinions?