Plus how much more tourism do they get?
And everyone wanting a 60k stadium, bear in mind that even if those 10k extra seats were sold out every game ticket income would only increase by 6-8 million per season. A modest hike in prices could generate 10 million, assuming they are all still sold. Considering revenue will soon be 200 million it's hardly going to transform the club. And obviously it would cost close to 100 million (current estimate for a seat for the 52k stadium is £7k and Meis has said the last 10k is always the most expensive) which would have to be paid back as well. For a 40 year loan it would mean 2,5 million per year plus interest, which would mean somewhere between three and four million.
Refreshments add a bit to that but since number of tourists at the match is lower than, say that other lot's, an average Everton fan don't spend as much at the match. Overseas fans visiting will spend money on scarves, shirts, programmes etc. They might buy a cuppa but just getting them to buy their pints from the stadium instead of a pub on the way to and from the match is a big task.
The big difference between GP and BMD in any case are the executive boxes. GP is desperately short in this regard. BMD can have plenty of them. And this is the real kicker. Club will be able to sell tons more boxes, especially because it's a new stadium at a great location.