Okay .... sorry if I am missing all the points but I am multi-tasking but have a need to see myself type stuff online
I have several sets of Vuelta wheels, which get bad reviews from a lot of people but not apparently from people who use them. I have also bought a set of cheapish ($500) Chinese CF wheels .... In all cases, I can say that light wheels are a huge upgrade over bad, heavy wheels. If your bike's wheels are in the 1400-1800-gram range, you might not notice if you just knocked off a couple hundred grams .... and you pretty much have to get lighter, more supple tires along with the wheels, which might mean more flats ....
And yes, when you sell your older bikes, sell them with the original wheels. No one will pay you nearly what any of it is "worth" (in terms of what you paid) so keep the good parts.
I weigh a lot and use way fewer spokes than people suggest I should, but even so I find my wheels last quite well .... so I can recommend cheaper, lighter, better wheels. You can spend thousands of dollars on wheels, or you can spend hundreds on wheels the cognoscenti will ridicule, but if they can hold up me (eighth of a ton) I pretty much I have to think you can get by with a great set of wheels for under $500 and keep them for years.