Well, similar discussions have been had on other threads on this site and while everyone remains civil I don't think there will be any resolution to the debate...
Anyway, first thing that's important is to realize that instincts aren't always simple things. We speak about them in really basic terms at times, but they can and do change depending on the condition of the animal, it's general health, age, gender and to some small degree (for snakes) constant repetition of certain stimulus... So... a well fed snake won't always react in an identical way as one that's hungry, warmer or cooler, night or day even gender can sometimes prompt different responses... It's also very difficult to apply totally identical situations more than once which is part of the reason we see behavioral deviations.
Now... depending on just which camps you choose to believe, snakes do have certain basic emotions- all animals do, but many of these emotions are just additional behavioral triggers... Snakes CAN feel pain, or fear and the abscence of pain and fear can be called contentment if not happiness, but there are questions which haven't been nailed down too firmly. Like... When a snake hides from a potential predator, is there any understanding behind the action or is it pure reflex?
My personal views place it just slightly more moderate than "pure reflex" and lean away from complex understanding. When confronted by something frightening, a human can conceptualize the danger, understand the potentials both positive and negative and that can either increase the emotions or be used to behave in a manner which counteracts them. A combination of my own experience and the studies conducted by others which I choose to believe tend to impress upon me that snakes don't have that capability. They react as instincts dictate, always and without fail.
So for us emotions are abstracts (Or, in the case of guys like myself, they are so abstract as to be almost nonexistant) they are more than simply a physical sensation, although there is that component as well. For reptiles they're more a survival trait... When something causes pain, escape it. When something triggers fear, hide from it or respond with agression. If the strategy is successful, the stimulus won't be there anymore and the behavior will return to a more relaxed state. If it doesn't, then the animal probably won't be passing on it's genes (including those which dictate instinctive behaviors).
Even though I have chosen a stance which I believe is correct, I can't prove it beyond ALL reasonable doubt. Nobody can, proving a negative (like the abscence of advanced thought) is difficult to the point of impossibility.
So with regards to your snake remaining inside or exiting it's hide when you enter the enclosure my stance is that the animal is simply reacting to subtly different stimulus, which prompt the changes in behavior. "Want" as a desire of something not immediate and concrete doesn't happen. This doesn't mean that your observations are without value, or even that I think they're entirely wrong... just that mine are slightly different and right. I'm not sure entirely how to word that in order to express the idea that my thoughts on the matter differ from yours and that I don't entirely agree with you but I'm not certain enough to start calling you incorrect.
Plus, look at it this way... You do know your animal. You know how it responds to assorted common stimulus and that makes you an excellent keeper because you can identify and analyze behavioral deviations very quickly and easily. In this respect putting our animals into human terms has an upshoot- just don't take it too far or you end up being one of those lunatics who starts rambling about how your snake only eats mice if you name the mice roger before feeding them off and enjoys those walks you take with her wrapped around your neck at the local mall because they "Love the attention"
"Genes, Like Leibnitz's monads, have no windows; the higher properties of life are emergent... And once assembled, organisms have no windows." - Edward Wilson, Sociobiology