You must have had a later one with upward facing caps, my original one spewed it's cap contents downwards all over one of the amp boards - that memory is the main reason I sent this one back to Quad for a full service before using it!
Don't worry about this as there is a kit from Quad to convert the caps to the later arrangement. (There used to be as I bought one and did the changes).
If the caps haven't been changed from the originals I would say that it is imperative that new caps are fitted for sound quality reasons and avoiding the corrosive chemical dump as described by Tony. If the output caps fail there is also the chance of damaging your speakers. Having said that It is more likely that the power supply caps will go first as they are more stressed.