I don't think the rise in sales in vinyl has much to do with the sound of vinyl. I think it is more to do with nostalgic reasons. One thing though is that they can only master up to a certain level for vinyl and they cannot really create a brick wall sound. That is one of the nice things about vinyl. You can also master a CD that way and still make it quite loud and avoid the brick wall approach.
I read a review once where they compared the sound of the Manley Passive to the UAD plug. They had a room full of engineers and switch blindly like 20 or so times and no one could pick a thing. So that sort of pretty well shows that software is as good as hardware, dont you think! People here who rave about how so much better hardware sounds would also not do very well in such a test, I can guarantee it.
You don't need million dollar setups to do mastering. Just some great knowledge and common sense and a reasonable setup (recording studio standard will do fine) Sure mastering rooms are nice but there is not a lot that cannot be accomplished in any decent room with a half decent set of monitors. Especially if you use reference tracks as a guide. If you have a beautifully mastered CD (from an expensive mastering suite) and use that as a reference for your own mastering and you are good at listening and comparing and tweaking your tracks to sound very very similar then in a way you are eliminating the less than perfect aspects of your setup out of the equation. And if you are wondering where do you get the reference tracks from. Easy, the client will always have them on hand. And they won't think any less of you for asking for a lend of them. Mostly they are impressed that you are wanting to achieve the same result.
I have mastered albums inside expensive mastering suites and many outside that environment too and you really would not be able to pick the difference between the two very easily.
I have mastered many many albums this way, been paid a lot to do it and have a whole lot of very very happy customers. That says it all and in a funny way it is a trick of the trade.