--Louvre in particular--I spent 1 week going in & out of this museum to appreciate everything inside.--I had a 4-wk vacay in Paris so I had alot of time.
--Venice & Rome---I like to feel like a local so 1 week in each city is good for me but if money is not an issue, I'd stay for a month.
--Carribean, Cancun, Mediterranean,Tahiti, Hawaii and any other islands---I need at least 1-wk to relax & enjoy, but if money is not an issue, I'd stay for a month.
To sum it up, I've done Paris in 3 hrs hitting all the major tourist spot using the metro. It's possible if you're just sight seeing and not lining up to go to museums. For Venice, some people can trek the island for 1-hr, I/my SO couldn't--maybe for a whole day of walking and a private water taxi--gondola is too slow so as other public trans.
I agree with you. As long as people have come this far, go see the Grand Canyon, one of the wonders of the world. And the only one in the USA>
Red Rock Canyon & Valley of Fire are worth a visit.
If people come here & only stay on the strip, that's what they saw the strip, but not Las Vegas.
People travel differently when they get older, they travel to enjoy. Not just mark something off as I've seen it.