A "better" PSU has less chance of exploding, that is reason enough for most. The PSU supplies electricity to a device where the slightest off spark can destroy all your parts. Cheapskate models will actually go so far as exploding in extreme circumstances and frequently lie about the power they supply, so they are really no better than a cheaper model with less power. Faulty PSUs can also cause random hard to pinpoint errors in daily use. It's not a matter of what you "gain" with a brand name, but a matter of what you lose with poor quality. More efficiency can be a good indicator since highly efficient models are giving more back to your system for their draw. Plus, electricity's expensive these days.
That being said, price alone doesn't determine quality, and going too far over with your wattage is a waste of power and really not great for your components either. Stick with well recommended brands. The priciest model of that brand is not always necessary, sometimes it is just a matter of savings on energy bills, quiet operation, modular cables, etc.