Is Luke a trustworthy historian?

I want to pick up a thread from my last post, one that I left dangling yesterday. I want to pose what I consider to be a very serious question.

Why is Acts written off today as a Lukan myth with little or no historical value? Why do scholars who wish to argue for the historicity of elements of Acts have to go through an inordinate amount of justification before doing so?

I ask this question for several reasons, reasons that feel schizophrenic to me:
1. When Luke uses Mark, he does not rework Mark as much as Matthew.
2. When Luke uses Q, Q-scholars tell us that he retains Q better in terms of verbage and order than Matthew. In fact, our reconstructed Q is versed according to Luke.
3. Luke tells us in the beginning of his gospel that he relied on older sources to rewrite the Christian narrative which we apparently trust given our hypothesis that Luke is a second edition of Mark.
4. If we think that Luke used Mark and Q as literary sources, wouldn't the best assumption be that he also used older traditional sources for the composition of Acts?
5. If 4 is valid, then shouldn't we be trying to figure out what those older traditions are and what they tell us about Christianity earlier than Luke?
I might add that many of the same scholars who are Q experts, are also the scholars who completely discard Acts in terms of any historical value.

I know that many scholars in the previous generation trusted Acts much more than is done today and perhaps more than it should have been. They didn't allow skepticism to be in the forefront of their scholarship; and more than not they were controlled by a Christian apologetic agenda.

But this doesn't mean that in response we should throw the baby out with the bath water. In my view, it means that we have to get back to the hard work of sifting through the actual primary text narrative to recover any historical nuggets we might be able to locate.