Your artifact issues are most likely related to extreme, possibly overlapping displacement. Multiple displacement shaders should be used care and displacement amplitude is best ramped up a bit slowly so you can see when it starts to create artifacts and dial it back. Noisy or high contrast displacement functions are also a common culprit.
Patch size *can* affect the fineness or scale of displacement, yes. One might call this a form of "detail", but it's not strictly a "detail" setting (i.e. "quality").
Regarding overall detail, that is definitely a complicated question, and for a couple of reasons. The most important issue, I think, is that different people mean different things when they use the word "detail", and/or they perceive "detail" (as-in render quality) when in fact it's more to do with shader complexity or just well-setup shading. A good, simple example of this idea is imagine that you have an "infinite" detail renderer with a bunch of high detail rock objects covering the ground. But the only shading is a neutral gray. Many people might say it "lacks detail", even though it's being rendered with "infinite detail". In a more descriptive sense it lacks accurate and complex shading, and changing the actual "detail" level wouldn't help.
That's obviously a very extreme example, but the same misconception or confusing word meaning often happens here too. People want "high detail" and hope that by increasing detail settings (like micropoly detail) they'll get that, or more "realism". But that's seldom the answer. Nature is complex and so complex shading (not necessarily complex in terms of the network setup, but the actual shading effects) is generally more realistic, even (and perhaps especially) when the complexity is subtle (e.g. multiple subtly varying shades of green depicting moss of ground cover, rather than just 1 color that is just distributed like moss).
Having looked at the examples I think you're referencing in the WM forum thread, I would actually say your images are *more* "detailed", but in a fairly noisy and chaotic way. Increasing micropoly detail will render your very sharp, noisy displacement areas with more "fidelity", more "accuracy", but I can all but guarantee that won't make it look better, or at least won't achieve what I think you are wanting. You should be able to get very nice-looking quality (and detail) with Micropoly Detail set at 0.7 or at most 0.8. With the newer Defer All rendering mode you generally need less micropoly detail as well.
I think you're on the right track starting over in a clean project and building from the ground up, piece by piece. Know what effect each and every displacement shader has as you go and you should have a much easier time tracking down any problems that happen down the line. And ideally do follow Ulco's advice to build from large-scale to smaller-scale displacements, top-to-bottom. Don't necessarily try to do too much with one node/shader either. You can have a very simple Power Fractal with just a few octaves giving you the basic macro shape changes you want, and then another below it adding smaller-scale detail. The amplitude settings for these may need to be very different to work well, and may need different displacement directions, etc. as well.
Oh and one more thing to consider: if you do want complexity, with multiple scales or types of noise or something happening in a single displacement step, consider building up the displacement shapes in *color* (grayscale) first by merging together multiple color shaders of various types, and then feed the output of that into a single Displacement Shader. The advantage of this is you completely avoid overlapping displacement occurring between the shaders that are driving the Displacement Shader. It doesn't mean that Displacement Shader will definitely not cause overlapping or other discontinuity errors when applied to a terrain with *other* existing displacement, but it definitely reduces the chances quite a lot and makes it all more controllable and less interdependent.
I hope that's helpful.
- Oshyan
