There are some differences in game play using upgraded balls, but no real need to make the jump. The main difference is how you plan approach shots. With the free ball you are unable to spin them with much success so they won't stop very well when they land on the green. Knowing this, you must allow for (more) roll. With purchased balls, spin can be applied to stop or even back a ball up. The more expensive the ball, the stronger its attributes.
Best advice, pick a ball, even the free one, and stick with that ball. The more you use a ball, the better you learn its attributes. Map the greens with your favored ball, consistently find the best landing spot, and sink those easy putts that you leave yourself.
As far as credits, use a smart phone or an emulator such as nox, to access the mobile app where free credits videos are more available. You need to"spend" time, but that could even be while watching TV. A half hour comedy is enough time to generate 100 credits. I use about one ball a day at a cost of 133 credits. I can cover this with one TV show and my morning constitutional.