Yes, beneficial refers to those genes continuing on into the future.

The operative descriptive word describing those "useless traits" is cost. If nothing else, they have a cost of the energy and resources required to produce the relevant cells or whatever. Another organism that does not waste that energy and resources will out-compete the one building the useless trait. Natural selection will make it go away.

Though that might just be the case for most things, I don't think it would be fair to say that for all things. Two traits could develop in conjunction with another, and trait 1 gives an advantage, while trait 2 is a disadvantage. The most in-your-face example I think is the stereotype of nerds and glasses. In short, a good enough trait could get you laid and fed even though you have a crappy trait that came with it.

edit: alternatively, a bad enough trait could completely derail the development of a good train. Maybe dolphins born with 200iq brains develop some other kind of bad trait as a result of the same mutation that doesn't allow for the 200iq trait to permeate.

The characteristic one for this in humans is sickle cell anemia. It really sucks for the people who have it but it sucks less than malaria, so it’s persisted in the gene pool… in regions with endemic malaria.

The poor eyesight you're referring to comes with age, generally after the primary ages of procreation. Conditions which cause poor eyesight from birth get weeded out.

That assumes that natural selection is a perfect process, and that we are at some "end" of it. In truth, the cost of generating useless noise could be small enough that it just doesn't matter and it hangs around. Maybe it will disappear in a few more billion years.

Any organism we see today may very well have unnecessary traits that evolution is in the process of removing.

You put that assumption in, not me.