I think the government works too capriciously as is -- because of the inflexibility I mentioned. It seems counter-intuitive, but it wouldn't be the first time that a well-intentioned, strong rule backfired -- causing the rule to be strong in principle but weak in practice (because everyone ignored it).
Passing laws is a real hassle in the US. They have to get a majority of votes in the house, 60% of votes in the Senate, not be vetoed by the president, and not be struck down by the courts -- and that's not even counting hurdles within congress (committees, leadership support, etc.) And you know what? It isn't needed. Many governments operate just fine with a parliamentary system that only has one real legislative body and a judiciary. In fact, well functioning presidential governments are quite rare -- and now we're seeing why.
What's the effect of a screwed up legislative branch in a presidential system? The executive branch taking more power (e.g. Obama's executive order wrt illegal immigration). That's now how it's supposed to work, but sometimes things need to get done, and if the legislative branch sits there, one of the other branches will take its power. In the longrun, it's dangerous. It's exactly the thing the checks and balances (inflexibility) was meant to prevent. Oh well.
Ditto with the constitution. The interstate commerce clause is used as the justification so much federal legislation, but it wasn't meant to be that way. The issue is that the constitution was not written with the needs of a modern government in mind. Rather than update the constitution (which is a pain in the ass), we warp the constitution to fit our -- often legitimate -- purposes. However, once we start bending the meaning of the constitution like that, it stops blocking the bad things it was meant to block.
Like all things, there's a happy medium between to weak and too strong. I just think that we're on the too-strong side.