Changing the wordpress comment section from nofollow links to no links will save your PR juice and you can spread it to other pages on your blog. Here is the tutorial to edit the wordpress comments to remove the hyperlink on comment author, but still retaining a website url credit to the author.
If you want to remove your WordPress category base to convert from domain.com/category/mycat1 to domain.com/mycat1, here is how you can do it. It is not available as an option in the WorePress admin, but using a plugin will enable this feature for you. Works for subcategories too.