About the useless casts of spells, I have no opinion because:
- it makes sense to have a system that gives you practice only when you cast useful spells, mechanics-wise.
- it also makes sense to practice by "uselessly" repeating casts, when casting is a combination of difficult gestures and sounds; as an analogy, combat is practiced mostly without danger, to approach perfection of movements, so as to be able to repeat them naturally in any circumstances. With experience, these moves become reflexes.
To me, it is a design choice to make, or it could even be combined, useful spells giving more experience, and spells cast under stress (i.e. combat) even more, for example.
One part of magic which I think needs more development is the glyph purification. This is, so far, of very little use: just making us lose a bit of time before researching. Maybe glyphs have been designed to "wear off", after all, and will need to be purified again in the future...