Well the first thing to consider is that the advantages will first and foremost be apparent with well recorded albums. A well recorded cd sounds better than a poorly recorded SACD or LP. One excellent site is
www.SteveHoffman.tv for determining the best sounding release of a given album. This could save you money in changing technology.
Advantages of SACD:
often comes with a RBCD layer (so one can rip it to comp or play it in a car)
is digital so the advantages of skipping tracks etc remain
small form factor
easy to use and maintain
can sound more holographic, better resolution/detail more dynamics etc. This is technology based, not absolute sonics.
players can be had for fairly cheap (Oppo universal for instance)
Disadvantages of SACD:
same small liner notes and artwork
can't rip the SACD layer, so no backing up!
Quite a few SACDS are merely RBCD masters on the SACD layer. So not cool.
Not many titles and it is a dying technology so the releases will be few and far between. Bluray is the next big thing with SACD likely to die a quick death.
Advantages of Vinyl
AMAZING back catalogue. Tons of albums never released on digital.
Large print liner notes and incredible artwork.
SQ is said to be more natural, holographic, detailed, solid, tonally correct etc etc. This is system dependent but there is a reason SACD was marketted as "more vinyl-like." No one advertises new vinyl albums as sounding more "cd-like" or more "sacd-like." This should give you a clue to how good vinyl can sound.
Vinyl is more popular than SACD and DVDA combined. Vinyl is not dying and is seeing a resurgence in popularity. Even if only a niche, it is a far healthier one than SACD by a mile.
Vinyl can be backed up. Sure it is not fun to do it (needle drops are not my thing) but it is possible and that means one can digitize their vinyl collection. very very cool.
Vinyl albums are often mastered better. This is not absolutely true but often true. Labels know that those buying vinyl want better sound and a good deal of vinyl is analagoue throughout the chain. Watch out for DDA releases. Might as well just buy the CD at that point.
Vinyl releases often come with a CD or a link to download a high quality MP3 version of the album.
Gear can be had for fairly cheap. The gear also scales up up up! And good albums keep pace with the gear.
Vinyl offers a more tactile experience, some see this as a huge draw. I do. It makes me feel more interactive and involved with my music.
Disadvantages of Vinyl
Dirty vinyl sounds awful. That means clicks and pops. One must clean their vinyl to have it sound best. Once cleaned, this means that vinyl can be as quiet as a CD...but it takes time and patience to get there.
Vinyl is more fragile in my opinion, again more care involved.
Vinyl is big and heavy. They take up lots of space.
Gear needs to be changed more regularly. Cartridge stylus replacements etc.