What if both of them put real effort (money) into research and arrived at similar/same place? Should it be dismissed as well? Or is there something as joint patent?
Independent invention should be a sign that the idea isn't worth patenting, that it was "in the air" at the time.
They don't, unless people use it and the patent holder wants to charge for licensing.
I don't have facts at hand, but I imagine that like any other thing (starting a business, writing a book, creating an App) 99.9% of patents result in no monetary gain whatsoever. But if we're going to go all in on the property aspects of patents, then I think that morally and ethically, we have to give an independent inventor a share of the property. Anything else just looks arbitrary, and leads to disrespect of patents, "intellectual property" and The Law in general.
Like naughty children, either you share nicely or nobody's having any cake!
:)
It still must be an enabling disclosure, though. That is, it has to teach the public how to make and use the invention.