If it's purely the question of cost per employee in favor of open office, why don't companies charge for private offices? I hope nobody actually believes that open office is measurably better in any other way.
I'm certainly not interested in paying/taking a pay cut to generate more value for my employer.
Well you are breaking your employment contract by not giving “best effort”.
If your management finds out, they should fire you.
Anecdotally, neither I nor my friends have seen this happen. Putting in more effort just leads to an increased workload along with a "Meets Expectations" during annual reviews. I have a great manager now but their hands are tied as far as bonuses, promotions, and raises go. It's a bad sign when the best benefit I get is that my workload isn't cranked up because I complete tasks more efficiently.
I'm still young, but I doubt that I'll see anything similar to a bonus or significant pay raise due to performance in my career. I still put in my best effort, but I don't see any reason to take a pay hit to get better working conditions if I'm not going to get rewarded later down the line like you assume will happen.
If such tradeoffs are offered by different companies, there is no reason why they should not be also offered as by one company.