I think a proper survey would be interesting to see. Most forums support that, or you could make one at survey monkey or the like.
Me, I've made over 150k salary for over a decade and I'm still too frugal to pay for business class outright for personal travel.
Sometimes on AA the miles to get it are not much more or the same as economy so I'll take the upgrade.
Just did a 14+ hour leg in economy plus for work and it was fine. power and enough room to open a laptop and I was able to get work done for 8+ hours.
The only way I can personally justify business class is an 8+ hour overnight leg and I try to avoid those anyway. I'd rather spend the money on a really nice hotel.
For work, economy plus has changed things so that unless you're a C-level exec or on a 8-hour+ overnight leg it's hard to justify the need.