I wouldn't mind if they did tweak the magic number and make it a bit harder and take longer to achieve the "perfect" team. The last 2 years the MN has remained almost the same, so they might be satisfied with it now and not change it any more.
The ability to get the perfect team is dictated not so much by magic number, but by the number of rookies (or rookie priced players) that establish themselves in first grade.
Even if you raised the magic number, guys like Cody Walker, Nathan Cleary, Jackson Hastings, etc would still have made a tonne of cash and everybody would have plenty of funds to upgrade for the run home. Raising the MN would make people more expensive, but it would also make price rises for these guys larger too so there wouldn't be as big a net effect.
If you want to make it harder to get a perfect team together then you'd need a major overhaul of how the money system works.
You could make prices subjective rather than objective. If you know some rookie is going to be his team's starting halfback from round 1, then price him accordingly. Don't just chuck him in at min price and give everyone free money. Or take a leaf out of premierleague fantasy and only give people half the profits when they sell. I'm sure there are other ways they could work it if they have the desire.
I'm not sure there is mass desire for change though - I think a lot of people would complain if they changed the status quo, more than would appreciate the changes, at least at first.