As you know, your contact list is your best asset... but YOU're allowed to receive mails from you... have they ever agreed with your terms? were they before signing up that you could sell that list to third parties?
Because if the answer is no then: a) those who buy the list from you will be spamming, thinking that they're not b) you'd be doing something illegal.
Abuse your list, treat it the wrong way and your best asset's value will be... zero!
I'd think it twice before doing what you pretend to do.