Is there a node that would improve the topology and even out stretched areas like the ones shown in the attached picture?
Short answer: no. This is so, because your edges are too hard. You may have to soften them a bit.
Is there any kind of smoothing node that could help out?
There is a smoothing filter, but it depends on what your main mask is made of. If it's a photoshop painted mask, e.g. that won't work. Blur in PS is then the best option. If you need hard edges for something again, you can always use the color adjust shader to harden those soft edges back.