As David Bayles and Ted Orland say in their quintessential treatise, Art & Fear: Observations on the Perils (and Rewards) of Artmaking, quantity is more important than quality. I love the story of the ceramics teacher who offered his students two choices. At the beginning of the year, they could elect to be graded based on the quantity of work, which would be weighed, or on the quality of the work, with just one perfect pot needed for that A. At the end of the year, all the best quality pots belonged to the quantity students.
Beyond the forward momentum boost, challenges offer creative community. Others are traveling the same path, sharing their insights. A step they take can pop a new idea into your own head and be the beginning of something exciting and rewarding. There's a sense of flow and serendipity that is beneficial.
Challenges can lead to new opportunities. Perhaps a new medium will come to your attention. Perhaps an exhibition will pick up the best of the challenge work. Perhaps a gallery or magazine editor will see your work as a result of increased exposure.
To truly keep the challenge pace, modifications may be needed. For example, the wrap ring at the top of the page was a deviation for me, due to a need to make something simpler and quicker than the other, more complex, rings also shown. It still fits with my body of work, but it gives me more options. I have loads of new ideas because of that change. I can't wait to try them out another week.