I started taking Flamenco to help with my Paso Doble and I found that what it really did was absolutely improve my arms and the way I used my hands.

A lot of the movements are similar such as the Cucarachas etc...in Rhumba. I thought it really gave me a good workout in skills that are easily ignored...that being said it needs to be a good Flamenco teacher or you really aren't going to get much out of it because the footwork doesn't really add to your ballroom repertoire.

Just my opinion...