This is one of those 役割語 that aren't used often in real life today, but I think it's more common than the almost non-existent ones.

My (male) university professor used to call some of his students this way. It was this usage:

親しみの気持ちをこめて自分より下の人を呼ぶ語。 「 －は長生きするよ」

お前 is intimate, and can be felt crude when used toward someone who isn't close enough. By attaching さん, he adds some distance, making it more polite. The professor just used お前 toward his closest students and his close colleagues.

I also know some guys who would use this phrase, mainly in senpai-kouhai relationships.

I have never witnessed this usage in real life:

妻が夫を呼ぶ語。 「 －，帰りにパンを買ってきて」

It might just be that you don't overhear private conversations between spouses so often. Also, this might be a class or regional thing. Personally, I sense the 下町 or 田舎 feel as a characteristic 役割語.

This one is only used in 時代劇:

相手を敬っていう語。近世，一般社会でも遊里でも用いられ，かなり高い敬意を表した。

This is very polite. お前 in this usage is the polite お前 so お前さん is double polite.

Mushi-shi happens to be one of the few anime I could stand and even loved. I browsed through a few episodes of the manga but couldn't find お前さん there. It looks to me that お前 is the default pronoun for ギンコ.

Most of his お前 is the casual, friendly, blunt, could-be-perceived-as-rude お前. Therefore, I can imagine him using お前さん as a way to soften this nuance in some situations.

This is probably different from お前さん I explained above because, for ギンコ, お前 doesn't necessarily signify closeness because it is his default language. Real people are more polite by default, making お前 stand out.