This is exactly why I decided to switch to the previous version of the unlimited plan. I have a 25% FAN discount and was at least able to save $15 off my monthly bill - the total will be $125 pre-tax, approximately $148 post-tax. In the 8 years that I've been using smartphones, I've never used tethering, so it's not a dealbreaker.
On a different note, knowing that I can be saving nearly $50/month with T-Mobile really makes me wish that their coverage was more reliable. I'd switch in a split second.
It looked like I had to option to apply my fan discount to the non tethering unlimited data plans but now it looks like those plans are completely unavailable