I'm thinking there is a middle ground for all this. I like Challenges, but do most of my geocaching while I travel. So, I like challenges that are not area specific. Ones that can be fulfilled all over the US and not restricted to a small area (collect all the geocaches in a specific city or county). Those small area challenges are restricted to a small number of cachers who live close enough to spend the time to complete them. So, challenges should be such that anyone can complete the challenge (spell out United States of America with first letter of various caches and only have to visit home cache to complete it or collect caches with colors from 8 pack of crayola crayons in them).
For souvenirs, you could incorporate a souvenir into some challenges (collect a geocache in all 50 states to get a USA souvenir, collect a geocache from all European countries to get the Europe souvenir, etc.). This sets up the souvenirs for all cachers and not s specific small group in a specific area. I also like the way they are doing it now for specific days that are not nation specific. That keeps it global and not US specific.
As a newby, this is my opinion and I know there are many old school cachers that have more relevant concerns.