It's not always that much more expensive but yeah sometimes the asks are crazy. A year ago I booked a flight on Virgin Atlantic in Economy and they offered an upgrade to "Upper Class" (their term) for $500 roundtrip to Europe per person. That was great value.
United has "Economy Plus" which is more legroom. I'm 6'2" and I find it fine. My advice is to upgrade to that and pay extra for the exit row. If there are 2 exit rows then book the one behind the one in front. You can't recline into an exit row so with the second set of exit rows you get a ton of space and no one that can recline into you.
I always upgrade to economy plus but it's only marginally worth it. Yeah, I can actually get things out of my bag (instead of smashing my face against the seat in front of me and fumbling blindly), but it doesn't solve the elbow room issue which is the real problem on planes for anyone of average build.
United has "Economy Plus" which is more legroom. I'm 6'2" and I find it fine. My advice is to upgrade to that and pay extra for the exit row. If there are 2 exit rows then book the one behind the one in front. You can't recline into an exit row so with the second set of exit rows you get a ton of space and no one that can recline into you.