Costs for renewables went down because of scientific and industrial/technological advances and yes political foresight helped. As for the subsidies, those won't be needed any longer, both wind and solar and viable without subsidy now.
Wind is close to viable, but still requires subsidies to get on par with Natural Gas (in the USA). Solar, hasn't a prayer of being viable in the near future. It generally runs 4 times the cost of Natural Gas (again in the USA).
You are wrong on both counts (in the USA), unless you define "viable" to mean something other than what most people think it means.. In other countries, Wind is at parity or better given the available options open to them (they lack the NG resources of the US), but this is not true in the USA yet, and I see no future scenarios where the costs of Natural Gas goes up and wind comes down enough to be at parity. Not to mention that Wind power suffers from one important problem, it only works when the wind blows, which is not all the time, so you have to build a fossil fueled plant to cover the load anyway.... Solar is so far out of the cost range it's not even funny. Even in the best conditions, solar is not a cost effective solution, even outside the USA. Solar's application is really for remote, off grid, low load use. It's not viable as a way to generate electricity on an industrial scale.
I don't always trust Wikipedia, but they have a fine article on this topic you should read. http://en.wikipedia.org/wiki/C...