Why torture yourself? Relax a bit. Spend a night in KL instead of going all the way to Penang in one day. That's what I did the last time.
Make sure you choose a good reputable coach. The last time on my way back from Penang to KL, the number of passengers from Penang in the coach was not "optimum" so they transferred (dumped) me to another coach in Butterworth where I had to wait for 3 hours.
When coming back to Singapore, beware of the tricks some coach drivers play. They are supposed to take you all the way to the final coach stop such as the Golden Mile complex but if most passengers alight at the Woodland checkpoints and you are the only passenger (or the only family group) left, then some coach drivers might play the trick on you on the pretext of waiting for the "other missing" passenger to come back. Either you wait and wait, or you get fed up eventually and take a cab back home from the Woodlands checkpoint.
If you don't mind these minor irritants (which may or may not happen to you), then by all means, take the coach and enjoy the trip!