Remember, there really isnt something as private domain registration as long as the LAW is concerned. Keep that in mind in case your venture is "out there". Registrars like Godaddy that provide private registration still are compelled to share information about the registrar in the event of a law enforecement probe.
I personally would never pay for the private registration.
If you have a portfolio of domains its a lot simpler to register a mailing address at a PMB or UPS Store. This takes away the risk of having your home address show. As for email privacy concerns, i just use a domain name for all my whois contacts. [email protected]. That way nobody's name is out there. Last, you can use the same officer for all contacts, and it can be anyone you want, including Rubplestilskin.
As for people marketing you based on WHOIS information. Its prohibited by WHOIS, but rarely does happen.