What does it matter whose wallet it is?
It does matter. What if its a big corporate's wallet? They will track you down anyhow if you try to hack their wallet. You will have to use an exchange to convert it into fiat and you'll get caught then.
After all, I have the dat file. all we have to do is crack the password?
Its not that easy if its not your wallet. You have no hint as to which type of password may be used there like "a name" or "a number" or both. If it was your wallet, you'd have some hints as you know yourself better.