...i.e. player whose motivation (morale) is higher, should receive more training points per one stretching/cardio/practice match.
If this is implemented, then probably the opportunities to earl morale boosters should be extended, since right now they are the biggest deficit.
By biggest deficit do you mean you constantly run out of them the most or the opposite? I know that I never get close to running out of them, so I can't see that if this was implemented there'd be any need to increase the places you can earn them - you can already earn 2 per match, and so can earn them at a far faster rate than rests and treatments which are more urgently needed.
Sounds like a good idea to me, it also would lead to managers spending more money, so we know Nordeus approves