A while ago I read something about how kids these days are too reliant on reward systems. They are praised and rewarded for every bare minimum effort they make.
While I think encouragement and positivity is great, I don't think kids should be rewarded for everything they do, or else everything they do in life may have the expectation of receiving praise or getting some reward from it at the end of the day.
Think of it as receiving criticism, which everyone needs a healthy dose of. Not criticism as in insulting them and bringing them down... but receiving feedback on what you're good at and what you're not doing so well at.
Sports for instance... these days, everyone makes the team, everyone gets to play, everyone gets a trophy. If my kid just absolutely sucks at the sport, I don't expect them to make the team, and if they don't make the team, I expect the coach to explain why. If not, I will explain to them that they just didn't have enough practice or experience in the sport, and I would encourage them to practice more and hope for better luck next time, and if they wanted to work for it, I would help them out with that. The reward? They achieve their goal and make the team...
Trust me, at the end of the day, I think a parent acting enthusiastic and supportive of them is much more rewarding overall than handing them a dollar because they didn't have any sick days.