Rock is more about the personal taste of the hobbyist. Some like a balance, some like minimal, others either side and lean towards more. More isn't a bad thing but it does take away from overall water volume. So you plan accordingly on what you want to keep and go from there. I favor a lot more rock but the tank has to be able to support it. More rock, more surface area for bacteria and other fauna to live. Also allows fish their personal retreat space. You sort of get the idea.
I guess what I'm saying is if you design your tank with all of this in mind you can have minimal, average, and a lot of rock to suite your needs. It isn't a direct answer but it really is a personal preference.