Þingvellir is great but it's mostly a natural site. It is, of course, historic, but I don't recall seeing anything physical there from Viking times
Most of the other items I have seen, they are cool, but they are replicas. As long as you are OK with that you should have a great time.
We drove past Snorrastofa on our way to a lava tube near Hotel Husafell , it struck us as being "another museum" (we aren't museum people when it comes to Iceland) that we didn't check out.