Even if these e-commerce giants start to accept bitcoin as form of payment, I doubt if that would bring the price up to unexpected heights. It is not as if those sites are exclusive to bitcoin. But that would certainly help in better circulation of bitcoin, and that is a win-win situation for both the buyer and seller.
I believe you are right.
A Bitcoin adoption by one of the ecommerce giants wouldn't mean a significant higher price.Maybe a slight one.
That would depend if these companies would immediately convert back to fiat or not.If that would be the case there could be an enormous selling pressure.
On the other hand it would bring a lot of mainstream awareness to Bitcoin, in a positive light, what shouldn't be underestimated.