Rach Già is one of the two ports where the ferry to Phu Quoc leave. The city is very spread out, but there is no real reason not to stay in one of the hotels next to the Pier. It's not a bad place fo a night stopover, but not probably worth to spend and extra day.
My mom was born in this city and although it is definitely known as the country south, it is rich in food and shopping. I heard from my parents that they've developed a lot and now you don't have to sleep at night with a mosquito net.