I can understand total trash (i.e. those levels that people often wish they could give below a one for, and ratings in that vicinity) being trashed. There are never too many good exemplars, and unfortunately, there are never too many bad exemplars, as some still have not taken a hint. An automatic mechanism like this could not be used without certain conditions, as it would most certainly be abused. It also does not help if all the reviews for the poor level were deleted because the levelmaker cannot get any tips, where they may have been expecting to review them at a later time, maybe even several times to become better. Their own caching of this information is not expected; after all, how many users do cache this information if they initially expect it to remain there? As such, if an idea like this is implemented, I would advise against making it an automatic mechanism.