I am of the mind that skepticism, properly applied, applies to everything equally so long as the thing in question is objective in nature (it is difficult to see how one would go about appreciating, say, art entirely skeptically). If you do not accept a factual proposition without evidence (or at least a good reason to suppose that evidence exists, since nobody has time to research evidence for everything) then it would seem unusual to pick and choose where you do and do not apply that methodology.

So, for example, I'm skeptical about fish in the same way that I'm skeptical about ESP - it's just that application of skepticism causes me to accept rather than reject existence claims about fish.

As for socioeconomics and politics and that sort of thing, then, I see no reason to apply the same methodology insofar as these things can be objective. The problem is that much of politics and economics is inherently subjective in nature. You cannot simply collect objective data on the 'goodness' or 'not-so-goodness' of any one political or economic system from scratch - you need to work with some subjective, starting principles of your own.

For example, you said you would be looking for a system that 'provides the best potential for a society and the happiness and success of the individuals that comprise it.' Well, in order to 'measure' that you would first have to decide on what a society would be like if it was reaching its best potential, how you would scale happiness and success of its individuals and so on.

Once you had that pinned down, you could apply skepticism by examining the effects of various economic and political systems through history and in the present day and seeing how those compare to your principles. This would be a difficult thing to do, because so many things aside from economy and politics could affect the 'well-being' of even a large group of people that it is difficult to isolate the thing you are testing. So you would never be able to get precise results in this way, only rather general trends.

Having said this, a skeptical eye may help you to identify certain political or economic trends which tend, all things being equal, to support your own subjective principles. Perhaps this is why there is so much argument on how to conduct politics and economic policy: not only are the are the features of a 'good society' themselves subjective, but it is also rather difficult to identify which policies are best at producing such features. So you end up with lots of people arguing about what they want and then, after agreeing on certain points, arguing again about the best way to get it!