The Taurus was a very solid brand for a long time. The product quality was quite good. Even Consumer Reports, that lapdog of Honda and Toyota, recommends Taurus as a used vehicle purchase.
Few people get excited about a Camry or an Accord, either. It's a bread and butter category. Performance sedan buyers are not comparison shopping the $40K 300M to other family sedans, like the 500. They are comparing them to BMW, Audi, etc. Different customer.
I think this is a smart move for the long term. You might not like the Taurus nameplate, but it has an established reputation that people who don't follow the car industry still identify with. In fact, what "Taurus" means to people who don't pay attention to the automotive world is far more important than what it means to people who do pay attention to such things (folks like us).
Is this meaningful in Ford's turnaround? I don't know. I don't think Ford has anything to loose by ditching a brand name that wasn't working (500), and not wasting time trying to develop another brand name. By all accounts, the 500 is a quality product. Ford has a marketing problem with the brand. This is a marketing step to try and fix it.
We'll see.