The thing with prepaints is that they're done at the fastest pace possible, and the paints often obscure some pretty decent detail on the sculpts.
I've painted on/over quite a bit of WotC Star Wars miniatures and I can confidently state that even a simple wash to bring out the details is a huge improvement over the original (pre)paintjob.
And some added highlights etc will pull a very mediocre miniature to acceptable or even good levels.
As an example, here's an overpainted WotC SW minis I did. I simply sprayed it white over the pre-paint and applied my own brushwork:
So I can totally see those Nano figures work. Especially since they're metal and can be easily and safely stripped...