Worst advice ever. Yes it is worth it, IF you have players to match the potential. You're fine with an advanced trainer, but should you have players who have superstar+ potential, then I would absolutely go for the superior trainer. It may make the difference between your player becoming a U21/NT player or not.
I myself have a level 6 trainer, I pay quite some money for it (65k a week at the moment), but my trainees are doing well, with my USA trainee who just turned 19 already at 63 skillpoints. He gets a lot of double pops, so I'm happy to pay this.