It's all about checks and balances. In a monarchy, if you have one monarch who is insane, the titled nobility would have an interest in removing him or her from power and deposing the family, thus becoming top dog. These wars need not be destructive outside of the aristocracy, see the War of the Roses. That threat of removal acts as a check against their power. In addition, a monarch has a personal interest in advancing the interests of the nation during her rule so that her heir inherits something better then what she got when she inherited. To that end, a free, educated people is a benefit to the monarch because they provide wealth and power to the nation.
Are you familiar with the tragedy of the commons? In colonial America each town would set aside a portion of land for a community grazing area. No one owned it, no one, therefore, invested in it or took care of it. The animals would, within a few generations, destroy it because no one person was in charge of it.
In our current system a President is in office for, at most, eight years. There is no incentive to make the nation better. For decades this wasn't much of a problem because there was the idea of serving something greater then the self but as we entered the post-modern age this idea has lost merit and now people sek out office not to enrich the nation as a whole but to enrich themselves. Everyone raids the kitty while not addressing the very real problems that face us. Everyone enters office and does what they want knowing that in, at most, eight years the problems they are refusing to address will be somebody else's problem.
As to spinning in their graves do you think that this nonsense we have now is what the Founders wanted? They fought a war over a tax that was a tenth of one percent. What's the percentage you pay in taxes? I guarantee it's more then that. Thomas Jefferson was a radical revolutionary. He never expected the Constitution to last this long, nor did he want it to, he was a firm believer in a little rebellion every few years being good for society because unless you are willing to die for it you don't posses it.
Look at it like this, the so called American Hero is always portrayed as an agent of the state, whether its a police man or a soldier the American Hero is always a tool of the government. Yet the histories of the people who signed the Deceleration of Independence reveal litany of pirates, black marketeers, speculators, and general malcontents. John Hancock, the famous importer in the popular histories, who signed his name the largest on the Declaration and who provided casks of wine to the rebels after they looted the governors house, made his fortune through the partial, and then outright, ownership of pirate ships that preyed upon British, French, and Spanish shipping in the Caribbean. Sam Adams, who is more or less ignored now, and who was the man most responsible for our independence would be classified as a terrorist today. Henry Lee, revolutionary general and father to Robert E. Lee, was a professional gambler and black marketeer. Paul Revere, when he wasn't involved in the silver trade, ran a counterfeit business on the side. The list is endless. The control, waste, and manipulation that is visited daily upon the American people is not something that the Founders would have liked. They would have fought against it.
They were not unified in their opposition to Monarchy, either. They were opposed to an absentee Hessian King (George the Third didn't speak English and was a German noble until he married onto the throne of England) who let his decisions concerning the colonies be influenced by the East India Trading Company, the Hudson Bay Trading Company, and those politicians that the trading companies purchased in Parliament, including the architect of the Stamp Act and the Townsend Act, Lord North.
As far as voting goes, the founders clearly did not believe tat the people could be trusted since senators were appointed and the electoral college was put in place to stop the country from making a mistake in who they elected. In the Federalist Papers there is a long essay about the electoral college. It was not supposed to be a rubber stamp but was a final check to ensure that the right person was elected. Thomas Jefferson famously distrusted the people to do what was in their best interest. In his private correspondence he often lamented the fact that people had been given the right to vote because they were too quick to vote emotionally rather then intellectually.