Why would Monarch want to operate a flight "just for enthusiasts". The A300s in their current config have 361 seats which is a hell of a lot more difficult to fill on the 180 seat A320s or 221 seat B757s/A321s.
The whole point of the enthusiast trips in the first place was to get additional revenue for the airline - I thought that would've been obvious! They don't do it for the sake of it, just to burn up some expensive fuel. Its a commercial operation.