Agree. When I am not expecting to use my Australian class one, I sometimes let it lapse, though never beyond the class two date. Never had a problem, though now that CASA keep the date of the anciliary checks like audiogram and stress ecg etc a close secret it is difficult to know what needs to be done until they tell you.
Suggest you do the basic medical, pay your 75 bucks and assume all is OK until they tell you otherwise. They have a whole department devoted to telling people otherwise.