what "higher income" ?
Do not fear about the price change, since ratio is based on income, so no big changes
i think the higher rewards from BGs are meant...

if a large playerbase recieve them regularly it will go up for sure
I do not like when people quote me out of the context. The paragraph you quoted says nothing about what income, it only tells you the basic about micro economic.
But in a matter of fact bg's are one of the parts scaling with level, but by end not the only factor.
But keep in mind that goldsymbols do have a 2x higher value when jumping 5 levels up on the scale.