Well, I can enjoy your levels with 2-3 players, but I start to dislike the gameplay after more players join. I should probably mention that for larger Instagib levels, players would need more incentive to play in all areas of a given level since powerups have lower priority and carrots have none. The only decent ways around this that I can think of is using multiple shields located far away from each and/or using coin warps (at a low amount) with shields.
(By the way, if someone remembers my coin equation, it would be greatly appreciated.)

I also agree that Instagib would work better with team games since players have more reason to use tactics.