What has that got to do with city fans having a(correct)opinion that money matters in the age of FFP? Using caps doesn't make your point right. No its not anyone else's money, but the club has a finite amount of money to spend because of the FFP rules, and if there are rumors that certain players might be given away, sold cheap, or in the case of yaya maybe even paid off...its not good at all, and people have a right to voice this opinion.
Maybe that hypothetical 6-8m for navas would mean having more available funds for players that are actually needed, and maybe someone is missed curved because of this defecit in funds. So easily dismissing it has potential knock on effects in the market for the club. Bottom line is its club money and that matters to club fans. Like anything anyone invests into in life...the financials matter.
Your willingness to so easily throw your insults doesn't help your argument.