Might selective reproductive instability be a factor in evolution?

Let me explain what I mean. The AIDS virus does a fairly poor job of reproducing itself, which turns out to be an advantage for the virus, because it allows it to quickly evolve and adapt to whatever is being used to treat it.

I am wondering if this principle might be a general factor in evolution. I am sure I am not the first person to think of this, but I have not come across any discussion of it.

To be concrete, let’s consider whatever it was that evolved into a giraffe. Suppose that the genes that determine neck length developed a strain that was prone to mutation. Most of the mutations are neutral or harmful, but a few caused the neck to lengthen and provided an evolutionary advantage in being able to extend the range of leaves that could be reached.

Among the mutations might be more reproductively stable copies of the genes, but the unstable copies would have an advantage in being able to cause further increases in neck length. This process would continue until the neck length approached its optimum size, at which point the more reproductively stable copies of the genes would win out.

This line of reasoning gives support for the idea of punctuated equilibrium. Does this make sense, or is there an obvious flaw in my reasoning? Have you seen a discussion of this anywhere?