So since I am incapable of thinking of anything other than fake science, I'm wondering what other biological adaptations vulcans have besides their extra eyelid (which many desert creatures often have)
First of all, let's talk about that extra eyelid. This is called the nictitating membrane, also known as a haw, and is primarily used to blink away debris. Camels, who live in the desert, use these to ward off sand from sandstorms along with their thick double eyelashes. Usually this layer is semi-transparent so when they walk through a storm they can still see where they're going. This seems pretty straightforward- usually this layer would be hidden in Vulcans due to the fact that we don't usually see Vulcans in a setting where they would need to use it, but it might appear when they are asleep or falling asleep (like in cats and dogs!) Vulcans might also have thicker eyelashes, sealable nostrils, and thick hair to keep sand out.
The pointed ears of Vulcans could come from another adaptation used by desert animals to cool their blood. Think rabbits and mice: they have large ears that they circulate blood through to cool it in the air. So if a Vulcan seems to be blushing at the ears, they might actually just be cooling themselves off.
It is also mentioned that Vulcans can go a long time without eating or sleeping, which leads me to believe they have a naturally slow metabolism or at least control of how fast their metabolism is. This is also common in desert animals. (Speaking of delays, animals can put off reproductive functions until they feel safe, which might have been why Spock didn't experience pon farr until he felt safe with the crew of the enterprise, but thats another post.)
Some miscellaneous facts include: Vulcans might have a tough digestive system, similar to desert pigs who literally just eat cacti, spines and all; larger feet to prevent sinking into the sand; and sleep in a crepuscular cycle to avoid extreme heat in the middle of the day and cold in the middle of the night.
And to settle the Spock runs hot/spock runs cold argument, unless you headcanon Vulcans as cold blooded they would run hot. It takes more energy to remain cold in a desert than it does to remain hot in a desert, and lucky for you spirk fans, running hot would mean that Spock was probably cold all the time and would ask for Jim cuddles anyway.
