Adwords Usage = Google Juice Correlation?

Wanted to see if anyone else has noticed that by having history in Adwords, Google will actually give your site(s) more merit for where it ranks after the campaign ends. Tried this twice now with some random niche based sites and the overall SERP ranking increased or sustained its position well after the campaign has ended. Months or even years later. In other words invest a few $xxx for a month or two to market your site, exhaust your available credit in Adwords, and then see long term benefits specifically in less competitive niches. Anyone else care to confirm or comment?

I've seen people saying it's true but never actually experienced it on my sites

Personally I think no. I have a few sites for which I am using adwords heavily and yet rankings do not seem any stronger for them than other sites wheer I am not using adwords.

Also I don't really see how it would benefit Google - its sort of like them rewarding you with a benefit that you are never aware of, for using adwords, so out of all the people using adwords only a very small percentage (that realise the correlation) are actually going to continue using adwords BECAUSE of that increase in serp positions - so I dont think it would make sense for them to do it.