Influential, yes.

Plato was an elitist to the extreme, and his notions of a rigid class hierarchy did shape early feudal civilization in Europe.

But most important? Would you want to live in his Republic?

Even more important, was Socrate's Republic meant to be taken seriously?

Elaboration: keep in mind the whole point of creating a city in words was to get a look at the soul, and Socrates hints at the fact the city wouldn't be practical in real life.

Can you explain how the Republic influenced the Merovingians?

Not sure what you're referring to there, but the feudal ideas of class determined by birth and lack of social mobility were adopted from the Republic (though the ruling classes certainly took some liberties in their interpretation; some analyses of the Republic suggest it wasn't meant to be quite so rigid).

You're simply restating what you said before.

The germanic tribes already had class structure before they crossed over into the former imperial territories. And in any case, every settled agricultural society in history (Egypt, India, China) has had so far as we know a rigid social hierarchy. That of medieval Europe was by world standards comparatively porous. So unless you can point to some specific evidence that the germanic tribes that ruled early medieval Europe were influenced by the Republic, we should assume that they were just doing what they would have done anyway.

FWIW, I do remember a reference to early Catholic structure based on the Republic, but it'll take me a while to go back and find that reference.

We've gone off-topic, though: the main point here is that Diogenes' own philosophy is worthy, even though society at that time found it less palatable than Plato's.

People ignored it (and still do) because it's less certain than Plato's "reliable" model of patterns, and also because it means giving up material comforts.