It's a single night. Just use it for one of the nights at the highest category hotel that you will stay in all year.

It has no value (actually, negative value) if you make a special trip just to use it. I'll usually make a couple of trips to a category 5 or 6 property every year, so the cert saves me 20k or 25k pts.

It has nothing to do with how nice the property is. Often, higher category hotels are just regular hotels in expensive places like SF or NYC.