I wish I knew what it was in the human brain that makes us so susceptible to this. It simply doesn't make sense to me. When I was a kid, I collected a lot of hockey and pokemon cards. It was awfully fun, so I can't say it was a waste, but it was definitely a money drain. Every last one of those is gone now.
For the outdoorsy types here in Colorado, it's collecting 14er summits. This is at least free, but it's pretty obnoxious when everybody has "the list" and people are always sizing themselves up by how many they've hiked. I find 14ers quite tedious and prefer other hikes.
Collecting travel locations is probably the most expensive thing you could do, but I'm talking international travel. National parks may not be a bad thing, but I kind of feel like you should want to go to those individual parks for good reasons, not just to check the location off of a list.