If you're renting out your spare room 70-100% of the time, why don't you just get a roommate? Seems like it would be safer, less work, and you'd ideally have a better long term relationship.
Lastly, we can have the room available for our friends and family when they come and visit (which is the point of having a guest room in the first place). My parent stay there (for free, of course) about 2 nights a month.
Here in my neighborhood, in Chicago, one can find a room for about $40/night; 15 nights and I already have half my rent. So yes, having a roommate might be less work (but that depends on what you consider "work") but I can make more money renting a room out by the night.