military buttons. Are only officers' buttons collectable?

[btns]

This weekend I came across a militia button, 25 mm (2nd Somerset; my guess c. 1855-c.1876). It is well made, but of the cheapest material one could order. I am not sure if it is pewter or tin-plated iron. Stamping its back with a name was obviously too expensive. There is no doubt that it is an 'other ranks' button.

Most buttons shown on this forum are high quality officers' buttons.
What is it? Do collectors go for shiny objects only?
Are other ranks buttons passed over or are they seldom found?
Let me have your opinions please.