Living your life by the concept of Value vs. Price is essential. By constantly increasing the value of your habits, relationships, and posessions, you are constantly moving forward, and increasing your pool from which you are able to pay the price of new value. For example, with all my extra time, I can SPEND more time to gain more value.
I like this idea, but I'm not so sure about the analogy of the money to living ratio... While you will most likely be healthier than the average 75 year old, would your 90 year old body really provide you with such a good quality of life for those extra 25 years? Yes, it could... but then again, you could get dementia or any of a number of ailments.
I'm not knockign your lifestyle in the slightest. Actually I quite admire it... but I have a feeling that for myself, I better get all my 'real' livin' out of the way long before I'm 75. Mainly because I have no idea if I'm going to be able to enjoy life at all when I reach that age.
Just my opinion though.