[How to make crisp, but subtle, seams]

I'd suggest, using voxels for larger points of detail, and switching to Surface mode to add the level of detail you're interested in. You could res+ your voxels, but your results will still be less crisp with the pinch tool or negative depth with a pointed alpha. Working with very high voxels rez starts to tax your system.

Play around in surface mode and and brushes, really nice differences in workflow there.

[FreeCAD 0.17 is released]

OnShape is free for the basic account, but know that all your projects will be public and accessible unless you pay for the license. Otherwise, it is pretty good, and is being developed by a bunch of prior SolidWorks devs.

[[Solved] Improve pinch brushes]

Pinch works as well as it can when working in voxel mode. Voxels, by their nature would not allow the pinching you are expecting. Switch to Surface mode, and see the difference.