"You explained how pleasure from our natural environment "caps out" past a certain threshold - I can't eat infinity sugar and derive infinity pleasure. So, obviously, my instinctive evaluation is that if I get wire-headed, I'll eventually get sick of it and want something else!"

I think you're lumping the concept of wireheading and the "experience machine" into one here. Wireheading basically consists of you pushing down a button because you want to, not because you like to do it. It would basically feel like you're a heroin junkie, but instead of needles it's pressing buttons for you.

The experience machine on the other hand is basically a completely immersive virtual reality that satisfies all your desires in any way necessary to make you happy. It's not required that you'll be in an orgasmic state all the time... as you said yourself, you may get bored with that (I just think of that poor woman with a disorder, that makes her orgasm every few minutes and she apparently doesn't like it at all). In the experience machine scenario, you would never get bored - if you desire some form of variety in your "perfect experience" and would be unhappy without it, then the machine would make everything to make you happy nontheless.

The point of the machine is that it gives you whatever you desire in just the right amounts to max you out on pleasure and happiness, whatever means necessary and regardless of how convoluted and complex the means may have to be. So if you're hooked up to the machine, you feel happy no matter what. The point is that your pleasure doesn't build on achievements in the real world and that there may perhaps be other meaningful things you may desire apart from pleasure.

As we've seen from luke, there appear to be at least two other human desires next to pleasure - namely "wanting" and "learning". But if the machine is capable of conjuring up any means of making me happy, then it perhaps would have to throw a bit of wanting and learning into the mix to make me as happy as possible (because these 3 things seem to be intricately connected and you may need the other 2 to max out on pleasure). But at the end of the day the experience machine is simply a poor thought experiment as I see it.

If you say I can be in a virtual machine that always makes me happy and then say I'm somehow not happy because I'm still missing important ingredient X, then that is not a good argument but you've simply lied to me about your premise - namely that the machine would make me happy no matter what.

However it doesn't really have anything to do with wireheading, as in the example with dying lab rats. That's just artificial addiction, not a happiness-machine.