Looks like it could be a strange atmosphere in WSU, where mainly only first couple of rows sold (with I guess few still to buy), when whole of rest of stadium pretty full.
Just to try to reassure you a little more, have just bought my ticket, and it states subsidised travel included, and gives link to the travel arrangement guide, which very much included Mill Road. There is no way its not going to be open on Saturday!
Many, many people will have bought tickets relying upon what the club stated in it's original press release. If Mill Road P&R doesn't now run people who bought tickets relying upon that statement should be entitled to a refund.
I would be amazed if some steward knows better than the club.
Not sure if your post was a joke I'd missed, but in case not, the original ticketing press release said "Park & ride will be in operation at the Racecourse and Mill Road."
Its definitely open and therefore chill (unless it was a joke).