Also gonna throw out there that I feel like cold media/roots and root hair death may be what leads to the cold spots on the leaves. Don't know how feasible this is, but I do it for African Violets: it would help if you had the option to use warm tap water to water your plants. Obviously it will cool to your GH temp over time, but you won't get the cold water shock that can really harm roots.
As far as the VFTs are concerned, if they awaken and you can reliably keep temps above freezing, nothing bad will happen to them. No reason to sweat bumping the overall temperature. The VFTs in the UGA collection are getting 65-75F nights consistently throughout the winter because they're grouped in with all the lowland tropicals like Neps and orchids. They emerge earlier, but there's no downside to this at all. If anything, by elongating their growing season I find they have better offsetting and seed set.