The switch shouldn't get hot. When it gets hot is caused be a bad/loose cable connection or a contact in the switch. Make sure all the cables on the switch are tight. If the switch still gets hot you'll need to rebuild the switch or replace it.
It wouldn't hurt. If the one your running now isn't getting hot it should be fine. What year and model is the cart? If it's a Marathon you may already have a HD solenoid.
I agree with HRC. Check it out after a nice 30 minute ride. If you feel some heat, that's normal. If it's way hot, be prepared to get an HD unit installed.