There are mixed 'reviews' about br 5.5 vs br 6
I personally feel that the version is worth the upgrade price ($40).
It has better terrain tools and better library structure. Handles memory better. Can use hdri lighting (very slow, but nice results). Those are the things I though were worth the upgrade.

DAZ Bryce pages, w/ more info:
http://www.daz3d.com/i.x/software/bryce/-/
Click on 'What's New?".

Friends don't let friends use booleans.