I have never had a set of iMac speakers fall apart and need refoaming. The best advice I have is to stop using them for music and get a nice set of cans.

In no specific order:

http://www.shure.com/

http://www.sennheiser.com/

http://www.audio-technica.com/

http://www.akg.com/

etc (I know I missed some)

And remember to stay away from anything Dr.Dre branded.

Gooing up the speakers may hold them together but you would have to be careful about what you use because that can affect the sound. If you still have your old wrecked sets then you might experiment with them.

Also, can you not use some nice quality external speakers?