Box Office: What If Movies success was measured in number of tickets sold rather than the gross earnings ?

This ain't just a random idea, its already being practised in South Korea, check there Movie Rankings below, especially the column Admissions

Will it improve the quality of content?

Probably Yes! As we see nowadays movies with no substance but big star cast and other buzzes, ticket prices are increased to encash on the initial hype before the word of mouth comes out, example Thugs of Hindustan. Also sometimes to hype the first weekend numbers the ticket prices are raised. if ticket sales also come out with the gross earnings then above marketing gimmicks will become irrelevant!

Will it reduce ticket Prices?

Absolutely! it would make the ticket prices reasonable at least, and overselling would be completely discarded.

Is it a more relevant parameter?

See the sales of Apple products are quite less than android i.e. market share,  Despite  Apple makes more profit. Though Apple products have high prices than Android, they have to be accountable too for quality same would apply to high priced movie tickets they would have to deliver the same quality. never the less, the crap movies that are branded as Gold now at high prices would be eliminated and filmmakers would be more accountable than they are now. Also, ticket sales would make the comparison fair between a small budget movie and a Big budget movie, because due to Branding, Big star cast and raised prices big budget movie makes more money!