Navigation as practiced by most wilderness travelers is fairly crude and based on a combination of simple compass work, and reading maps and topography well. Before you get your knickers in a twist, consider that engineers, foresters and geologists for whom sighting compasses were designed are using the numbers generated for data - not for getting from point A to B. For that, they often lay the mirror out flat and use them (hang on to your hat) like regular ol' base plates. I still think that for the rest of us they're overkill - but what the heck.
Just out of curiosity, can anyone supply a story about actually needing the sighting feature for navigation? For that matter, can anyone pose a scenario for which they are even hypothetically necessary?
As for accuracy, each style has its pitfalls. Standard base-plate compasses are best used at belly-button level and are mostly prone (in my opinion) to errors of carelessness - especially if you're taking bearing after bearing in low visability / heavy brush. To use a sighting compass accurately requires practice and care to avoid parallax errors, which can be significant. Pick your poison.