At a certain point realism won't add much more to the game. In all honesty the chances are absolutely zero that people will recognize "Wow, that rubber is simulated really realistically". It either looks real or looks fake, and right now you are looking pretty real.

There may be some physics glitches, but at the moment its a pretty fun simulation. I think that friction and bounce are more than enough to finish up the physics, after that I think interactivity (Of the table) becomes more important.