Does shady spectacles also copy a cards tags? So if I have breakneck mech and copy a plaza guardian, will the plaza guardian get the bonuses from breakneck mech?

Yes — Tags are copyable traits, so the equipped unit copies the chosen unit's Tags along with its Name, Type, Cost, Domain, and Rules Text (Rule 477.1.b.1.a).

But the follow-up depends on which unit is wearing the Spectacles. If Breakneck Mech is the equipped unit and it copies Plaza Guardian, it stops being Breakneck Mech entirely — it keeps Mech as a tag (Plaza Guardian is a Mech), but it loses Breakneck Mech's own rules text, so "Your Mechs have [Deflect] and [Ganking]" is gone and nothing else gets that bonus.

If instead Breakneck Mech stays in play and some other unit copies a Plaza Guardian, that copy is a Mech (Plaza Guardian's tag is copied), so Breakneck Mech's anthem does apply to it — even though the copy's own printed text is now Plaza Guardian's.

One caveat: only printed/copied traits are copied. Keywords granted to the copy target by another card's ability aren't part of its copyable traits, so a unit that's only a Mech because of some other effect wouldn't pass that along.