I agree with most of what you said, however I believe that alt coins are sort of a sandbox. I believe in BTC and am sure it will continue to rise, however I believe that it is not flawless and another coin will emerge which will supplant it. Surely that coin will come from the alt coin scene. Currently there are a few alt-coins which are not scams which are actually trying to gain acceptance. Currently the alt-coin scene is like the wild west, it is completely unregulated and tons of scams are abound and everyone is looking for an instant get rich scheme. However, there are people out there that can and will innovate. Those that truly believe in digital currency as the future, not merely as ploy to confuse people with technical jargon in hopes of getting them to hand over there money. The people who do that (I won't name them here) infuriate me. They are detrimental to the broader acceptance of crypto currency.
I agree with you, especially regarding the snake oil salesmen pushing this garbage. It is possible that an alt will steal the show, however I believe this would only happen if Bitcoin absolutely crashes due a technical problem which makes it unusable. Chances are the Bitcoin codebase will simply be tweaked as the years pass in order to solve these problems before they become insurmountable. It reminds me of TCP/IP. It has a tremendous number of inherent flaws and is demonstrably inferior to new, competing network protocols. However, it will remain the basis for the internet for some time to come simply because of its adoption rate. So, I think the most an altcoin will do is provide a research environment for desirable features to integrate into future Bitcoin.