(Serious question:) What, specifically, do you see that's new in the past 233 years that we can learn from? Aren't most democracies created since 1787 also extremely flawed and/or mostly copied from the American Constitution? Hand-waving that "it's been 200 years, there must be better ways to do it" without actually providing any is not something I find particularly convincing.
In any case, I think a lot of the problems you're describing are not strictly constitutional, or at least lead to contradictions if you try to fix them.
* It's very hard to keep courts from becoming politicized unless either everyone acts in good faith (ha), or you figure out a way to pick judges that doesn't ultimately get its power from elected officials. The lifetime appointment idea is about the best I can think of for that - even something like a single 20-year term has the problem of kickbacks after leaving office. For a long time, the requirement of supermajority approval was also a really good moderating idea, until McConnell realized that he could win by default by just not doing his job. Maybe a combination of large supermajorities and forced votes? But all of this runs into the problem that one party simply does not want the government to function. It's relatively easy to design a system that prevents people from doing something; it's much harder to design a system that forces them to do something when they benefit from stagnation.
* Executive power will always ebb and flow as laws are passed, unless you disallow Congress from delegating its own power, which would be silly.
* Legislature is at an impasse - I mean, if you have disagreements on the order of 40% of the population thinking that large minorities shouldn't be considered citizens, then I'm not sure how you can get past impasses. This is a symptom of hyperpartisanism, which is itself, I think, a symptom of poor education and misinformation. People disagree. You can't force them to agree unless you a priori give some of them power over others, which kind of defeats the point.
As for what's good - I think most people are also fans of the 4th and 5th amendments, and the 8th gets a reasonable number of references even in casual conversation (even if people don't know which one it is). And the 13th-15th are all pretty damn important.
The Constitutional structure as a whole is pretty good. The things I can easily think of that I /don't/ like about it, and which haven't been cleaned up in amendments, are:
1. Senate apportionment. Corn shouldn't get a vote. Admittedly, this is pretty major, but it would also be very, very hard to change in a new Constitutional convention, since even if you first agree that the Constitution should be rewritten, states won't ratify a new one if they feel like they're losing power.
2. Lack of clarity on what to do when there's a criminal in a position of power. It's tough, because any procedure can quickly become a farce if you make impeachment and removal too easy, but it would be nice if at the very least there were some minimal enforced procedures with regards to witness testimony and debate. And we could maybe strengthen the bit about the House having subpoena powers with a "yes, that means you, Donald."
3. Mandate better voting systems for Congress. As it stands, states are free to, on their own, adopt proportional representation (at least in states with sizeable delegations; Wyoming can't), ranked-choice voting, or any of the other better-than-first-past-the-post ideas that political scientists and mathematicians have come up with. This doesn't /have/ to be a Constitutional change, but it might be better if it were.
4. Mandate a formula for resizing, not just reapportioning, the House after every census. 435 is not enough to capture the variance in sizes of states without severe compression, and leaving it up to Congress to make itself more representative is a bit of an oversight.