I would definitely recommend this, especially for your boys. The fireworks are amazing. I presume you have seen the descriptions on this webpage?
We saw Rhine in Flames from St. Goar last summer. There are three ways to experience this: you can buy a ticket on a riverboat, and see it from the water (which would be a little pricey). Or you can try to book a hotel room in Rudesheim with a view of the river, and watch the fireworks from the balcony of your room. Or you can join the crowds and see it from the riverbank. That's what we did. There were lots of people but it was not overwhelming. People started staking out their viewing spots around 6 pm. We had light rain off and on for a couple of hours. Everyone crowded into restaurants and underneath awnings when the rain would start. So if rain is forecast, I recommend you find a sheltered place early, just in case. The fireworks started around 9:15 pm and lasted for almost an hour. It was truly spectacular. I would do it again in a heartbeat.