If creating a CDO creates more value to the economy than designing an automobile why shouldn't engineers focus on building those?
People forget that prices and money are essentially information about the supply and demand of a good. As we progress in the information age deriving information from price will consume and produce ever more of our GDP. Spending money efficiently and directing it to the right purposes is a VERY valuable thing for a nation to do. Perhaps, dare I say it, more valuable than engineering widgets.
If YC had engineers figuring out algorithms to determine the best startups and they found one that worked it would be a very valuable piece of information. Or more relevantly, what if you had a site that required a lot of bandwidth and you could buy a bandwidth future? If you could buy that sort of thing you could offer 4 year contracts to your customers with out taking on any risk.
How about this instrument, a YC Summer 2014 startup future, it estimates the expected return from S14 and pays you if the return is less than expected. YC could sell them today and gain the advantage of knowing how many startups they could fund in S14. It would allow all sorts of people to pool their knowledge about what the Summer 2014 startup scene is going to be like. You might want to buy one right before the S14 season because you know that some great startup is applying, etc. If you held office space in SOMA you could use this as a hedge against losses incurred due to a poor S14 startup season.
Most complicated financial instruments are actually risk mitigation and/or information pools. The fact that that kind of thing is pricable due to these engineers spreads all sorts of great information to our economy that you can use to make informed decisions about how to conduct your affairs and you don't even need to participate in the market to use it.
Want to know what the best guess as to the price of oil in 6 months? Check the oil futures market. This one number contains the all the information known to man, vetted by experts as to what the supply and demand of oil is going to be in a few months. It also allows anyone with new knowledge to monetize that information and communicate it to all participants almost instantly. Southwest can offer cheaper flights because they use oil and jet fuel futures to buy jet fuel, the brilliant thing is that Exxon also gains knowledge of what Southwest and every other airline expects their passenger load to be in a few months and can make decisions accordingly.