4k in general is worth it but that has nothing to do with SU10 or DLSS.
With DLSS the experience is worse than with TAA as it’s a downscaling/upscaling algorithm which draws textures and details more blurry - it’s basically useful on weak GPUs only.
Other than that the overall picture quality did not increase as there are still no DX12 effects used (reflections are still screen space reflections, not “ray traced”, shadows are implemented as on day 1, volumetric lighting did also basically not change from a technical aspect)
In general there is not a big issue going 4k even on RTX20 cards with MSFS - your CPU will be the limiting factor most times 
Benefit of 4k is compared to smaller resolutions more fidelity especially on large screens due to less aliasing and finer details being visible 