I will say her most recent cover album art makes her look trashy??
 It's all relative.  Compared to Britney she looks like a Prom Queen. 
Marketing (not necessarily her choice?) has made her what she is.  I think she has a great sense of lyric phrasing and timing, even if her voice is not technically the greatest, but it reminds me of what happened to the very good guitarist George Benson - the guitar disappeared and the focus was on white suits and vocals and no guitar. 
Although she is no Bill Evans on piano, I would still like to see this Berkeley graduate who studied under some of the greatest jazz educators strut her stuff a little more on the piano. 
BTW, although I am not an Elvis Costello fan, I did enjoy his hosting of one of Marian McPartland's Piano Jazz shows (with guest Allen Toussaint), and Elvis is a fan of the jazz genre.
http://www.npr.org/2012/08/31/112183772/allen-toussaint-elvis-costello-on-piano-jazz Steve