If you aren't using the iPad then its not worth keeping at all really because its just dead money gathering dust on the side doing nothing you might well get the money for it and get something else or the new iPhone 5
You have to ask yourself am i going to use the iPad if you aren't then its not worth keeping at all really.If you use the iPhone a lot more then you would use the iPad the maybe buying the iPhone would be a better option for you depends what you use.
I have both iPad and iPhone and i use both everyday for several things so i get my use out of both device because they are using both daily but if i wasn't then i would consider selling the device which i'am not using at all there no point keeping something if it stuck in a draw doing nothing and losing money on it.
hope that it helps