i've seen cat power about 6 or 7 times since 1996. twice, she has been absolutely terrific, and both times were with backing bands (in 1996 with steve shelley and tim foljahn, and in 1998 with jim white and mick turner of dirty three). only once when i saw her completely solo was it good, and that was in 1997. the last few times i've seen her solo, it was pretty miserable. she fucks up all the time, apologizes, starts and stops songs, etc.
this should be a good show because she has a full backing band of seasoned musicians. she gets less freaked out when there are other people to hide behind.
i'd only go if you were wealthy and absolutely love her records. at $25+, my instinct is to say stay home.