If for whatever reason, one has to absolutely travel on the booked flight in a lower class, my vote is that at the very least cash compensation should be offered based on the fare paid verses the cost (that was available on the date of booking) of the class travelled.
In 2007, due to a tech problem, SWMBO and I, along with all the other pax were bussed to The Roosevelt Hotel In New York for a night, we were fed and bussed back to JFK the following day, we were given seats in the J cabin albeit not in the seats that we had originally selected and travelled to Sydney via Brisbane. The Sydney to Brisbane leg in a 738. No compensation but just happy to travel in the class booked.