@Mark Belew I agree that multiple touches has always been key for any marketing effort. I personally think that 7 is a bit excessive as a "standard". The real key is getting the right audience. In some areas there are too many investors mailing to the same absentee owners. I don't see how your mailing is going to stand out from all the others unless you do something different.
Some possible additional groups can be:
Seniors with long-time ownership: These guys are often ready to downsize out of the big family house or transition to some sort of senior living facility.
Homeowners with Low Financial Stability Scores: If they tend to be financially unstable, chances are good that they will be looking to get out of a mortgage.
Both these groups probably haven't updated or kept up on all the maintenance so you have a good chance at a lower purchase price.
When you mail, you can put in benefits of working with you rather than the traditional sale. Consider something like this: "Are you ready to sell your house but think it will be too hard to fix everything up first?"