[Gadget]

I think that when you 'sweep' your leg, pose or walk, then a straight leg and pointed toes adds to the style and grace of the dance. As to having bent knees, in my (limited) experiance bent knees help to maintain balance when spinning or doing a turn with a step.
If you have been trained how to spin with your toes/feet and can move where you are being led, then I don't see how it can be detrimental to your dancing. I can 'feel' some difference in dancing with someone who has classical training, but this is more in the fact that they come out of a re/turn perfectly balanced and with little or no momentum - when you are used to everyone else's body following the spin, it's different.