I have a mid-fi SACD (I was suffering from Catalogue-itis at the time!) and SACD built into my new DVD. It's definately got better sound quality than CD, but I doubt I can hear half of it with my mid-range cinema system. The 5.1 stuff is used as more novelty than anything else on some albums where they pan sounds around your head, and positioning musicians around you as if you were in the same room as them.
Remastering 2ch to multi-ch is also somewhat dubious.
There are a few where they use the surrounds "properly" - live recordings where the sound engineers set up mic's around the room to correlate to the 5 speaker positions. This results in the ambience and "air" as well as higher definition on the recordings thanks to the high resolution DSD recorders.
This results in subtle ambient sound coming from the rears and great soundstaging across the front 3.
These recordings are where SACD comes into it's own as a serious format.
Unfortunately you will mostly find these recordings on Audiophile labels, while other record labels mostly use the surround effect as a gimmick. Still it is fun to hear sounds flying over your head, and moving around the room etc
It's worth remembering that there are far more 2 channel SACD's out then 5.1 and a lot of those are serious, novelty-free audiophile quality recordings.