This is more like a conservative investment in various things by the managing funds for 200 years, followed by a reckless investment in the cities of Philadelphia and Boston at the end of 200 years. It probably didn't do particularly more for the people 200 years from the time than it did for people in the interim.

Also, the most recent comment by cournot is interesting on the topic:

You may also be using the wrong deflators. If you use standard CPI or other price indices, it does seem to be a lot of money. But if you think about it in terms of relative wealth you get a different figure [and standard price adjustments aren't great for looking far back in the past]. I think a pound was about 5 dollars. So if we assume that 1000 pounds = 5000 nominal dollars and we use the Econ History's price deflators http://www.measuringworth.com/uscompare/ we find that this comes to over $2M if we use the unskilled wage and about $5M if we use nominal GDP. As a relative share of GDP, this figure would have been an enormous $380M or so. The latter is not an irrelevant calculation.

Given how wealthy someone had to be (relative to the poor in the 18th century) to fork over a thousand pounds in Franklin's time, he might have done more good with it then than you could do with 2 to 5 million bucks today.