To be more precise, ROI, calculated as (gain from investment - cost of investment) / (cost of investment) does not go down with time, unless you generate losses over the years.

Also, I think this could be more precise than my list.

I'd also think it would be difficult to precisely estimate all costs that will be paid at closing (e.g. prorated taxes) so that seller literally walks away with exactly the amount you discuss with them. 

This is precisely why I specialize in a niche or two. 

There will be varying levels of precision, but it will help you understand where to focus both your time and your capital.

Where as the auctions the inventory comes to you in a nice precise manner with professional sellers who are motivated IE banks..

Just keep in mind unless you're exclusively using a single marketing method that there is absolutely no way to determine precisely that media/message's return numbers.

Spell out precisely how the offers should be submitted.  

To be entirely precise in my question, what have you guys seen to be the best type of marketing piece (and content) for elderly owner occupants? 

Foldvary points out that the cycle does not always function on a precise 18 year schedule, but - baring catastrophic events like a world war - for the most part the cycle should be right around 18 years.