So, my personal view, I do think we will over-estimate the impact of a stadium - if you look at Juve's matchday revenue, its actually pretty close to what Inter make right now. Of course our new stadium would be a larger capacity, etc, than theirs - but I think expecting a +35-40mil uplift from the stadia is naive personally. I guess the lack of paying rent may help a bit, too, but that's only a small impact.
The thing is, for 400mil (each), +35 mil isnt actually that great an investment in many ways.
The problem with our financial situation is that to get the CL revenue, we of course need to spend like a CL club. Our revenue now is way higher than it was 5 seasons ago, but so are our costs, so exactly as expected, being in Europe has increased the amount of money we can spend - the problem is we're still paying for some poor decisions that keeps us financially unhealthy (Dalbert, Lazaro, Correa, Vidal, etc)
There are some things that we can change (wages, amortisation basis, our sponsors, even our stadium, etc), but there are some things italian football and italy as an economy needs to systematically change - like the league's international presence, TV rights, etc.
If, over the last 5 years, we executed perfectly and didnt have bad signings, etc, we would probably have been about break-even before COVID
You need to spend big, but you also need to do it on a sustainable basis. By sustainable, I dont mean 'decrease costs to match revenue', but 'increase revenue to match costs'.