I see it as a problem if honest driven newcomers are disillusioned and driven off (or just lost in the noise) by cynical low-grade money grabs that didn't actually earn their place.
This doesn't happen. Very low quality games are already being accepted via Greenlight constantly in a fair way. It simply doesn't happen that a good game gets lost in the Greenlight noise in this point in time. What does happen is that a shitty game that got through Greenlight doesn't sell a lot once it gets released on Steam, which is the natural course of things. A few years ago getting through Greenlight was a win for indie developers, because few would be able to. But now anyone with a half decent game can get in.
Scammy games make it in, and then they use those same scammy practices to get high ratings on the app. Suddenly, these obviously terrible games are getting enough attention to show up on my radar.
This won't happen on Steam because the PC market is different from mobile. Games are expected to be longer, more complex and cost more. This means that the PC audience is more likely to search thoroughly before buying something, while on mobile it's all free, games are simpler, and the audience isn't really engaged in doing their job. Valve can add curators, tags, reviews and other user-driven stuff because it works well on PC since the audience is much more engaged in their entertainment. This means that it's considerably harder to game the system in any reasonable way to fool people. Let's assume you make 100 fake positive reviews for your game. ALL it takes is a few people to counter this, since reviews show up on your game's front page based on how many people agree with it or not. Most people won't agree with your fake reviews, but will agree with genuine reviews that are negative instead. This warns anyone who has a brain that there's something weird going on with the game. Just look at the latest example, Titan Souls: http://store.steampowered.com/app/297130/
It's better for the developers we want to support and it's better for us from the customer experience.
It's not. Tons of developers who have good games wouldn't have been able to get on Steam prior if it was more closed, simply because it would still depend on whoever the curators are (which back then was Valve). Valve doesn't get a say on what games their customers like, the customers do. If you think that doing some work into what you're buying is too much then I guess you just have to get used to the direction Valve wants to go in. They give you the tools to look for things and you look for them.
If I'm looking to purchase a game under $5.00, for instance
There are many other ways to look for games on top of that, like based on genre, popularity and so on. You just have to kinda know what you're looking for I guess?