Miss-and-out (eliminations) is a great spectator race. We do it to three people left. Neutralize the race for a lap and then make it a 3-up match sprint for the finish.
The scratch race can be fun if done right. The secret is to award money on each lap. We had the Alpenrose Velodrome Challenge a couple weeks ago, and the scratch race featured $2 for the first across the line each lap and $1 for the second. It basically ensured that the race was full bore for the full 15 miles.
Match Sprint is a great spectator event as well. Two or three riders, three laps, first one across the line wins. Run it as a ladder or as a round robin.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter