Yes, Red Bull will care about the difference between 2nd and 3rd for sponsorship purposes, but there’s no way that McLaren would have beaten Ferrari so it’s a moot point for the rest of the grid. There may still be people at McLaren (and other teams) who remember the 2007 spying scandal and see this as an opportunity to serve a bit of that back at Ferrari. Can’t blame them really, this does look pretty dodgy.
I’m not sure on this “technically legal” thing…
The legality is determined by the fuel flow meter. If that says that it never exceeded the limit, then the case won’t stand up in court. It’s definitely very fishy, but if the FIA can’t prove it was illegal, they can’t disqualify the car.