I think prestige and overall image of the club and stadium are critical for long-term success in the top flight - look at Brighton and Brentford since building their stadiums, they've never looked back
Also if you want to grow the fanbase you need to make sure there are ample tickets available for casual fans who are unlikely to bother with building up their loyalty points, sitting on season ticket waiting lists, etc, etc
They just want to be able to easily jump online, buy a ticket, and enjoy a one-off game with low / minimal effort
So it's multi-dimensional and not just about raw gate receipts or number of bums on seats
It's complicated, some clubs have what is now prime location for development enabling them to raise funds to build new out of town stadiums, for others the costs of leaving a 20,000 stadium and going off and spending many millions to build a 40,000 capacity place just don't add up even more so if there is a danger of relegation once or even twice.