I think SACD is like any other format. While in theory, SACD should be superior to RB, such is not always the case - just as every LP is not automatically superior to every CD. It depends on the original source of the music, the care with which the record company chose to make the transfers and the skill of the manufacturing company that produced the finished product.
That aside, SACDs made from pure DSD sources can be a remarkable thing and therefore a worthwhile addition to your system. The air and the transparency can be breathtaking. But don't look at it as a contest between RD, SACD and vinyl. There are times I want to listen to CDs, times for SACDs and times I want to listen to vinyl. It all depends on my mood and the quality of the particular source material.
Now for the bad part - IMO, based on owning several players, SACD players often do not reproduce CDs as well as some much dedicated CD players. I found this true with both the Sony XA9000 and the Esoteric X-05. You might consider picking up a Sony XA 5400 just for SACD, although I hear the RD is pretty good too. I have heard that the upper echelon players such as the X-03 or Meitner have superb CD reproduction, but I have no experience with those players.