I see your points and appreciate your comments. These ideas are definitely a jumping off place, not always great, and because I assume I'll have to wait some time before JC notices, I'm not about to dump them all at once, and attempt to let them build off each other. With that in mind I have an overhaul for Food and Gluttony planned which should make these changes a bit more meaningful. The gist is a switch from purity and an over-emphasis on certain recipes at the exclusion of many others, to a quality based system. In that system spoiled food is simply not as effective as quality food which makes spoilage less harsh. Additionally I'm only proposing this for uncooked foods, so generally any food used in a recipe will not be affected by spoilage. I think processes Fruit Food should also be exempt from spoilage.
A high Thermal is definitely not a difficult barrier, nor do I think it should be, I don't envision the need for adding special shop items to compensate or the need for two torches (I do see very rare areas where are impossible to stay on permanently without such means, but they would be only at extreme cold spots the edges of the map). Essentially temperature is an excuse to reduce grinding by increasing gains, which should be available and obtainable to everyone who plays, although more appealing to mid to late game players.
Spreading out Fruit would indeed be a pain, but Fruit needs to be nerfed in a meaningful way, and this is more creative then hitting the numbers, and theoretically less random than a proposed tree disease. The counter to this is that while it will be more difficult to get all the fruits, they will spoil slower than they currently do if temperatures are cold enough or stored in a root cellar, making this barrier not insurmountable.