Re: Over engineered?
Not OVER engineered. Just engineered well.
Philae fulfilled her primary objectives (get to the comet, touch down, deplete batteries while gathering as much data as possible.) That is what it is engineered for. That engineering then allows her to continue operating for longer than just the primary objectives and fulfill later research as well.
Just like opportunity and curiosity are doing and spirit did. That doesn't mean they are over engineered. Every mission like this has primary objectives (we'll do this first), then secondary, tertiary, quaternary, quinary, senary, septenary, octonary, nonary objectives after that. The hardware is designed to be absolutely sure it'll fulfill the primary objectives, very likely the secondary, probably the tertiary, maybe the quaternary, perhaps the quinary, etc.