Well, ok, fine, it's not a "must", but it sure is nice. It's saved me plenty of time and annoyance - not just at train and public transit stations, but also at museums and self-checkout supermarkets. Yes, these occasions might be 2-3 times per trip, but before I got that card I had several experiences of having to wait ages for a ticket agent. It's not the most fun way to spend even a part of your vacation, if you can avoid it.
And applying for another card is not going to have any lasting effect on your credit score - that is why there are thousands of credit card churners with excellent credit ratings.