Misting the leaves won't hurt as long as you do it in the morning and the leaves are dry by the time the temperature starts to fall. I don't think there is any advantage to misting a Miltassia, or other members of the Oncidium alliance. They generally have fairly tough leaves. I would recommend the use of barbeque skewer to test the moisture in the pot. Fortunately, Miltasias can take a little more water than some other orchids, so I think you will be OK so far. I recommend reading this post of mine on skewers:
Skewer use for watering of orchids