Yeah, good question. Mastering consists mainly of setting EQ, and making it consistent throughout the album, applying compression, and setting master volume. At 58, my ears are pretty much unreliable. What sounds good to me is a lot of highs, but this sounds too brash to most people with better hearing. Compression is a tricky thing, the right amount sort of glues everything together, too much makes everything sound kind of muffled.
Garage fans like a rawer sound than regular humans, so we're sort of disabled in that way. In the end, I'd say, Mastering: Yes. Then there's the little issue of finding someone who knows what they're doing. Different people will produce a different sound. Your mileage may vary!
