No. There's absolutely a gain. A big one, too. The main reason it isn't done today is not that it isn't useful, but that it's too slow to run e.g. bcrypt on the client without native browser APIs. WebCrypto will change that by adding PBKDF2 as a module accessible from JavaScript.
The main reason we encourage people to use key stretching algorithms on the server is that, if an attacker gets access to a database of password digests that aren't very strong, they can trivially be reversed.
Doing this key stretching or "password scrambling" on the client side simply moves the processing burden from the server to the client. There is nothing less secure or less useful about it.
There is, if you don't again hash the passwords on the server. This is why new password-hashing proposals like [Catena](http://eprint.iacr.org/2013/525.pdf) include an official "server relief" mode where the majority of the hashing is done on the client side, but there's still a final server-side transformation step.
Until such time as these things are readily available, recommending that people do client-side hashing is absolutely going to result in trivially poor implementations.
You might want to consider that if these problems were as trivial as you seem to believe, there would already exist a library vetted by cryptographers to do exactly that.
The main reason we encourage people to use key stretching algorithms on the server is that, if an attacker gets access to a database of password digests that aren't very strong, they can trivially be reversed.
Doing this key stretching or "password scrambling" on the client side simply moves the processing burden from the server to the client. There is nothing less secure or less useful about it.