I propose to have no sliders and employ a "hover over preview" system for settings. Hover over preview is, in my opinion, the best way to work.
HOW WOULD IT WORK
Instead of having to click and drag a slider we would simply have hover over the area where now the sliders reside AND when hovering over the effect would be previewed in full screen (same behavior we already have for Develop Presets)
Then if we want to commit the value we click. A small circle would then appears at that value position as reference and the numerical values appear on the side as usual.
I made a mock-up UI where you can compare my idea vs the existing UI.
This system would be incredibly advantageous compared to sliders. Previewing is extremely advantageous and with the step-marks we would be able to get/jump to the value we want much faster and more clearly than now. Also we would be able to have/set a value BUT at the same time preview a different one to see the difference.
E.g. Set Highlights to + 100 Hover over Highlights +50 to see the difference...if you prefer +50 just click.
Much better than now, much more versatile and time saving.