Keywords is a very slickly implemented feature that is great for doing searches or using rules.
But, for the specific purpose - delineating different versions of albums - I've found "Description" to be more helpful, because A) I can create a column in Playing Now for it, and b) I can put any type of version information in it.
So, the Description field can be " Redbook layer from 2009 Hybrid SACD " or "XRCD 2011 Remaster by Alan Yoshida" or "2010 Analogue Productions SACD converted to 24/88.2 FLAC" or " Vinyl Rip of original 1966 US Pressing " etc. etc.
That's true, but it depends on what you're trying to accomplish. I use the description field to specify what version of an album I have, as you have shown above.
But when I'm just wanting to see all SACD tracks, Vinyl Rips, Bonus discs etc. I find keywords to be more useful because I can just search for "kw=SACD" or "kw=Vinyl" for example.
The reason you don't see any tags for SACD in my screenshot though, is because I ended up borrowing a PS3 to rip my discs and they are all DSF/DFF files, so I just have a library view that only shows that type.
I should probably add a SACD keyword to them for the sake of consistency though.