One point that isn't directly mentioned is that he was able to turn the 'wobbling plate equations' into a Nobel Prize because he had such a wide breadth of knowledge to draw from, and probably had a habit of drawing parallels between what he's doing and other things within that breadth of knowledge.

He wouldn't have even thought to make the parallel between the wobble and how electron orbits move in relativity if he didn't already have a good understanding of electron orbits, and it wouldn't lead to the Dirac Equation in electrodynamics without him being familiar with that, then quantum electrodynamics without being familiar with that.

So yes, while play and working on things 'with no importance' can lead to great discoveries, or something of importance later, you need to have that background of knowledge and the habit of connecting two disparate concepts together or else it will always remain something 'with no importance'.