Here's a video of my latest run, 148 points at level 21. Not the top of the leaderboard, but I'm pretty proud of it. The way I'm kind of mentally strategizing is while I'm faster than the other runners, saving nitros and getting boosts at all costs. Once the other runners are faster than me, I only burn nitros when I'm out of the top 6. I broke my own rules in level 9, though, diverting just before the finish line to pick up a boost that was way off track, and then burning nitros so I'd be able to catch up before the end of the race; I don't know if it was worth it.
Accepting less-than-first in the later races means a lower final point total, and I don't really prioritize coins at all. If I was just going for straight points those would both be mistakes, but I'm really trying more for levels - by playing that way, the nitros last longer and I can pretty reliably get to 20+.