The point is that pornography and masturbation are forms of sensory stimulation that mimic the desired real world outcomes (finding a mate) without actually leading towards them.

Humans do desire finding a mate. However, they also value sexual pleasure and looking at naked people as ends in themselves. Finding a mate and having sex with them is obviously the ideal outcome since it satisfies both of those values at the same time. But pornography and masturbation are better than nothing, they satisfy one of those values.

I think you could say that about practically any example. You could say that people watching Friends are fulfilling some of their values by learning about social interaction - rather than just feeding themselves a fake social life in which they have really funny quirky friends. You could say that ladies with cute dogs are fulfilling their desire to love and be loved - rather than creating a fake baby to satisfy their maternal instincts. We won't find a perfect example, we just want a pretty good one.

Wireheading is kind of like this. Wireheading is when an agent simplifies its utility function for easier computation and then continues to follow the simplified version even in instances where it seriously conflicts with the real utility function. I don't think pornography is an example of this [...]

Me neither. I was trying to characterise the pornography problem - not the wirehead problem.

most people will drop pornography immediately if they get a chance at real sex. This indicates pornography is probably a less efficient way at obtaining the values that sex obtains, rather than a form of wire-heading.

Unwillingness to replace the fake simulation with the real thing (if it is freely available) isn't really a feature of the pornography problem. The real thing may well be better than the fake simulation. That doesn't represent a problem with the example, but rather is a widespread feature of the phenomenon being characterized.