DryToad

Thanks for the replies, everyone! @BoltBait thanks for reminding me that tool existed, I guess I was thinking so much about curves and levels that I forgot about the basics. @MJW, do you have a magical box from where you take out a plugin for every need I have? Sadly, the scanned documents I wanted to enhance seemed to have some very dark pixels scattered around, so the changes it made were near to none. I ended up going with @ardneh's tip. Using the levels tool wasn't so difficult after someone told me what slider to use (thanks dude), and once I realized I could use the histogram to figure out where to stop. Definetively using your plugin for other projects tought, having a task automated is always great!

Thumbs up on MJW's plugin, a plus is that it works for bigger clusters too! On that note, I just found out that G'MIC has several filters that help a lot with this kind of cleanup.

Let's say I have an image made with white (0), gray-ish white (64) and gray (128). What inbuilt tools / plug-ins could I use to "rescale" (I have no idea what's the word for this) these values so that I use the full range, ending up with something like 0, 128 and 255? (I suppose levels does that but I have no idea how to use it, and if there is a plugin that does something like that I would like to know) Many thanks!

If anyone stumbles on this topic searching for a plugin that does that, archip's Stray Pixel Remover works wonders. The Number e's Cluster Clear should do something similar too, but I couldn't make it work.

Man, I have been looking for this plugin for AGES, thank you so much guys. It's great for removing leftover dots after using ArgusMagnus' Unblend.