Generally speaking, yes. Keep in mind a lot of Holiday Inn Express properties don't really have much they can upgrade you to, so there's not a whole lot they can do in terms of upgraded accomodations. In general the better properties will be able to treat you better because they actually have suites and club lounges they can upgrade Plats to. Of course it comes down to the policies of the specific properties, but I'm sure for the most part if you're nice at check-in and ask nicely you should have pretty good success.