I want to say that I heard somewhere (mind you I have no facts to back this up) that realistically potatoes arent horrible as long as you counter act it with fat (lots of butter, sour cream, etc) I wouldnt make it an every day thing of course, but trial and error doesn't hurt in the long run. I'd say if you absolutely have to have mashed potatoes or the world is going to explode, then by all means allow yourself mashed potatoes every now and then.
Do you track on my fitness pal? Maybe figuring out what a standard serving of mashed potatoes comes out to, and then taking that into account with the rest of your meal planning for the day?
I can sympathize on a lot of the things that you mention as well (poor money management skills (it comes from the belief that I have a foreshortened future, yet I'm still here so you would think that I would learn better), binging episodes (eating primally and especially LCHF has helped a lot with this), I'm a food horder, etc etc etc) I just have to keep reminding myself that it is about the journey.
Its hard when you want change and you want it now...lol thats where patience comes in