Technically measurement devices are described by wavefunctions too.

Well, yeah, maybe. There's a reason that the Measurement Problem is called what it is.

I'm replying here since we appear to have reached the end.

Presumably measurement involves interaction with 3 or more degrees of freedom (i.e., an entangled pair of qubits and a measurement device). This is something, for most types of interactions (exclude exactly integrable systems for the moment), classical or quantum, we cannot analytically write down the solution. We can approximately solve these systems with computers. All that to say, is that any solution to any model of an 'individual' measurement will be approximate. (Of course, one of the key uses of quantum computing is improving upon these approximate solutions.) So what type of interaction should you pick to describe your measurement? Well, there is a long list and we can use a quantum computer to check! I guess part of the point I am trying to make, is when you open the box of a measurement device, you enter the world of many body physics, where obtaining solutions to the many-body equations of motion IS the problem.

> We can approximately solve these systems with computers.

Yes, but with quantum measurements you cannot even approximate. Your predictions for e.g. a two-state system with equal amplitudes for the two states will be exactly right exactly half of the time, and exactly wrong the other half.

I guess I don't have an issue with being wrong if we treat 'measurement' like a black box.