Challenges can definitely help you focus. And if you are at all goal oriented or competitive, they are great motivators...even without actual payoffs outside of knowing that you kicked some serious ass.
One more thing I do when shooting street: if I’m in an area with homeless people or street buskers, etc. I will often carry small bills or change. And I frame that as appreciation, not payment. Sometimes a little respect and conscious eye contact is all someone needs. I see my camera as my eye. When I photograph someone, I’m saying, “I see you. You matter. Thank you for being here.”