I actually think that it's the other way around at the moment. Steam provides a community for many games that wouldn't otherwise have one as well as increasing accessibility markedly... Not to mention the Steam achievements, trading cards, and whatever else they decide to put up as a Steam-wide 'meta-game'. Steam does add value to games. It's why it is so popular in the first place.
As I said earlier, it's my personal opinion that it's the other way around. Steam's recent decision to create an Olympic size swimming pool out of early access games has resulted in some rather sub-par games making it onto the broad market. All someone needs is a promise and something that is remotely playable in any of a thousand senses of the word and they can put it up on early access or greenlight and reap near-full rewards for an incomplete product. Should Steam decide to limit the number of games that can make it onto early access and greenlight to encompass only the games that are generating the most hype, I believe that a good balance between quality and quantity can be reached.
StarMade has been greenlight for a long time now. The reason we're not marketing on Steam yet is that we feel (especially with our payment method likely to change down the line) that our game is not ready to be advertised, as it's changing dramatically every month.
Hope this helps!