Funny part is, till season 4, I didn't even know that there is a total stadium upgrade. I used to upgrade pitch, lights, seating and other facilities but not the stadium as a whole. Then I noticed other's stadiums are better than mine so I checked my stadium page and saw the upgrade button next to Stadium Level 0. That's when I upgraded it. LOLs......
BTW, opponents Q does affect the attendance at home matches as there was a thread in which the basic formulae for the ratio of ticket price to attendance was given which included the current form, opponents Q, our own Q, ticket price, etc. it was tested and held true for many.