At least it should spike up into the 60% range a few times a day. But you asked what is optimal, so 60% or more is. Yes, a consistent 50% is too low, but you can correct that by misting.
No, if your humidity is correct, you don't need to raise it for the shedding cycle. You'll know if the humidity is too high, because you'll see mold, smell mildew, or have too much condensation inside your cages. You'll know if it's too low because you'll see your snakes shedding in pieces.
I live in a rain forest (redwood forest) and I still have to humidify my snake room. I find the better caging you have, the less of a battle this is. Where it's dry, it's near to impossible to have the right humidity in an aquarium, on the other hand in a moist climate, with sterilite or rubbermaid tubs, you have to poke extra holes in them to let some of the humidity out besides the ones for ventilation. If you have a nice professional plastic cage, it's pretty easy.
I don't spray my cages for humidity, I humidify my room. I want my breeders to think it's the rainy season when I mist them.
I have a friend who lives in Las Vegas and she keeps boas also. She was always trying to insulate her room better and get bigger humidifiers and all that. When her snakes grew bigger she got some professional plastic cages, and now she swears by them, for the way they stay humid inside.
Some places are more challenging than others. Wherever you have to heat a room, it will dry the air. I spent a lot of money on a big overkill cool mist humidifier, when it turned out, all I needed to do is make tea in my room. : )
Good luck
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Caden Chapman
slithering.serpents@gmail.com
http://slitheringserpents.com