Considering the sheer number of cars in GT, it does surprise me we don't have a more robust set of organizational tools. A certain other racing game allows you to create different groups within your garage, naming them anything you want, and then populating them based on your own personal choices. This is far better, to me, than having to work within PD's predetermined categories (Standard/Premium, sorted by make/year/etc etc). For example, I have a "Drift" group that has some mightily disparate choices in it, cars that never could be grouped together if we only had GT5's methods to use.
That said, it could be improved; instead of groups, as someone has already mentioned earlier in this thread, PD could use user-generated filters to let us sort our own garages. The problem with FM4's groups setup is that a car can only exist in one group at a time; with filters, that wouldn't be an issue! 👍