German pre-dreadnoughts were poor carrier-conversion candidates

Should Germany have converted its pre-dreadnoughts into aircraft carriers?

No, unless the conversion could also deliver a major speed increase through extensive reconstruction.

The answer rejects a superficial conversion that simply places a flight deck on an elderly battleship hull. Carrier aircraft need wind over the deck, making ship speed a central part of launch and recovery performance. German pre-dreadnought machinery could not provide that margin in its existing form. Only a reconstruction extensive enough to add several knots could produce a useful operational carrier, at which point the economy of reusing the old ship becomes doubtful.