As many others have stated, alternatives to cash payment are helpful, especially in younger age groups. Helps show a non-monetary mission and also get involvement. This can include fine forgiveness coupons (as prizes or earned), reading, community service.
While not dealing with any of your goals, online payment has helped with payment of fines. Some now just keep it longer, finish and then pay the fine since it is convenient. Not sure if this keeps holds manageable with patrons not rerequesting things they didn't finish, but likely leads to some longer loans.
One option I haven't tried but have been thinking of is more on the encouragement side in the return courtesy notices (almost due). I've been trying to find the article but there was one regarding putting statistics on receipts like trees saved, etc when people failed to bring their reusable, etc. It was worded well not to be insulting but places saw an increase in customers remembering. It was adapted to other places as well. I would be curious if any library has tried similar with notices stating how many people are waiting for the item and encouraging returning early if finished. Our current ILS doesn't make this easy since it is dynamic but hoping to try it out in the future.