should parked domains be submitted to search engines, worked

[webmasterbeta]

Hello all! This is only my second post so forgive the complete n00b question and my lack of SEO skills, but - I've been purchasing domain names from time to time that I think (hope) will be valuable some day.

Thanks to my lurking around digital point for a while, I finally decided to give parking a try based on comments of many people monetizing their idle domains in their domain portfolios.

I've parked my domains and have adsense on them- should I try to build up their PR by listing the domains in directories and working on backlinks, or should I not even waste the time (since there is no "real" content other than the adds relating to the domain names)?

Thanks!