Why shoot them down? Ask for money.
There's good money to be made in developing ideas that you might not see the value in but someone else does (possibly rightly!).
There's good money to be made in developing ideas that you might not see the value in but someone else does (possibly rightly!).
But you do have a good point about someone else possibly seeing value... however, many of the ideas I've been approached with are of the form "like Twitter, but for Poker players!" or something similarly silly.
The problem I see with these types of projects is that they are typically championed by people who have no real understanding about how software is developed, a la clientsfromhell.net. Those are situations I just don't want to get involved in.
It's a win-win because they'll either leave you alone or pay you lots of money!