observation - Could science be lost if a phenomena is observed before predicted?

An observation could validate the predictions made by a previous theory. If something unpredicted is observed, then a new theory which is compatible with the observation should make predictions which later are confirmed by new observations.

But what if no such new predictions are possible to make? What is the scientific status of a theory which after the fact is only compatible with all data, but which cannot make any new predictions? If it would be considered weak, does this mean that discoveries through observation can actually destroy science?

Is this a valid argument for delaying the construction of better observatories until theories have matured given all existing data? Kind of comparable with the forward planetary protection argument which says that human spaceflight to Mars should wait until it is certain that there's no life there which could go extinct when it meets Earthly life.