I'm also wearing my SB with my XMTS kilt in this pic (though you have to look close to see it). I don't think it looks the least bit "costume"-y.

Personally, I don't feel any constraints about it's history or origin. I think it's just a good looking belt & wear it any time I d**n well please.
Ah, but Red, you're not wearing the part that "makes" it a Sam Browne, namely the strap that goes over the shoulder. I think that's what most of the objections are about, since a true Sam Browne is an article of military kit.

This extra strap was specifically designed to carry the weight of a side-arm, hence its association with military & law enforcement uniforms. Without said strap, it looks completely different.

T.