The reason there tends to be less accumulated/leftover stench from pot is because the frequency and volume is much much lower than cigarette smoking.  

With great frequency, a pattern like the one on your wall tends to be water flowing toward the wall instead of away the wall at the surface.

The frequency could be any where from weekly, bi weekly, monthly or any other way you can think that coincides with your mailing campaign.

But I'm wondering what other resources are out there that others are using and at what frequency. 

Since frequency is important over time (until the property sells or the deal is done), does everyone send the exact same letter/post card month after month?

You can set the notices to come at the frequency you select.

What do you recommend as far as frequency of mailing? 

If you intend to mail for an entire year, for example, and send a total of twelve letters, decide the frequency of the mail drops and test response.You could design a campaign that hits heavy early and then takes a rest then starts hitting heavy again after a break.Test, test, test!

I'm worried that thinning my list down will reduce my chances of landing a deal but I should be more focused on my mailing frequency and be confident in my mailing list.

For most homeowners a 7 to 10 year fixed ARM will work, given the average frequency of moving.