I think there is an additional way in which "bucket list" culture has changed :
When I was a kid, in the 60's, travel was a big thing - big expenditure, big effort in planning, info was gathered from travel brochures spread over the table, long-distance phone calls had to be made to check things (or you had to be sure you had a reliable travel agent), and there was all the trouble of foreign currency and travelers' cheques. You didn't know when or if there would be a next time, because it was all pretty hard to get organized and funded.
So when you (your parents) finally did the trip, it was an achievement, something you could be proud of, and could consider yourself lucky to have accomplished. Of course you'd take photos of the major monuments, with yourself beside them, etc., because it was a personal dream come true.
Today's over-running of popular tourist locations is just, imo, the evident outcome of travel becoming easier, population growing, and popular destinations staying the same size.
I think that one of the main things that make the smartphone so popular is that it is just the modern-day version of worry beads : a tactile way of being detached from yourself, much better than staring aimlessly out the window of the bus or train, sinking into a difficult chain of thoughts. And if it's smart enough to keep you connected to other people, then the next logical stage is to project yourself outwards, instead of sinking inwards. Yes, in some cases even incessantly - and what better projection than a selfie?
The future of human existence on the planet has never before been so obscure, so let's be more tolerant to one other, even to the obsessed selfie-takers - there are still enough places that we can go where they won't...