An AI could be made to wirehead easier or harder.

Probably true - and few want wireheading machines - but the issues are the scale of the technical challenges, and - if these are non-trivial - how much folk will be prepared to pay for the feature. In a society of machines, maybe the occasional one that turns Buddhist - and needs to go back to the factory for psychological repairs - is within tolerable limits.

Many apparently think that making machines value "external reality" fixes the wirehead problem - e.g. see "Model-based Utility Functions" - but it leads directly to the problems of what you mean by "external reality" and how to tell a machine that that is what it is supposed to be valuing. It doesn't look much like solving the problem to me.