Aaaaaaaaaaaaaand here's the results:
Assuming no roles to interfere other than the following:
Doppelganger
Townie
Spore Spreader
This program assumes total randomness for lynch, non-Dopp for kill, and non-infected for infection. Infected players infect on lynch.
Variables: 16 Town, 4 Dopp, 1 SS
Dopp Wins: 7536 Spore Wins: 2005 Town Wins: 459
Variables: 16 Town, 3 Dopp, 1 SS
Dopp Wins: 5685 Spore Wins: 3177 Town Wins: 1138
Variables: 16 Town, 2 Dopp, 1 SS
Dopp Wins: 3619 Spore Wins: 3796 Town Wins: 2585
Changes to rule set: Infected players no longer infect on lynch.
Variables: 16 Town, 4 Dopp, 1 SS
Dopp Wins: 8473 Spore Wins: 927 Town Wins: 600
Variables: 16 Town, 3 Dopp, 1 SS
Dopp Wins: 7131 Spore Wins: 1423 Town Wins: 1446
Variables: 16 Town, 2 Dopp, 1 SS
Dopp Wins: 5193 Spore Wins: 1699 Town Wins: 3108
NOTE: Changing player number to 15 will more accurately judge win rates, but assume a slight increase in Spore and Town win rates and a slight decrease in Dopp win rates with 15. I'm too lazy to check all of them at the moment.
Effectively, this is just a bunch of stats of what happens in the game with no modifiers. Sure, the roles balance the game in favor of town, but these don't have much effect on the Spore Spreader. Tech Shields are relatively uncommon, and you can merely decrease the win rate a max of 10% to adjust for them.
The Spore Spreader has no counter play other than killing or blocking the Spore Spreader, which, in itself, is tougher than saying so. The Dopps can be protected against, investigated, blocked, lynched, and killed. The Spore Spreader has difficulty being found out, wins long after death, increases his chances of winning with his lynch or infectees' lynches (which is the Town's biggest weapon), and can actually make the game unwinnable if left to his own devices (which a third party usually is, since he's not the main focus).
I don't want another role that's not fun. This one isn't as broken as the Ghost or Watcher, but it's still broken, and the game's fun could be at risk.