If I increase a units might by 5 and then attach shady spectacles do they become a copy of the unit with the extra 5 might until the end of the turn

Yes — the +5 stays. Shady Spectacles only replaces the equipped unit's copyable traits (name, type, tags, cost, domain, rules text); Might increases and decreases are applied separately in the Arithmetic layer, so a temporary +5 on that unit keeps applying on top of the copied Might until the effect's duration ends (FAQ #11745, Rule 477.3).

So if you buff a 3-Might unit to 8, then equip Spectacles to copy a 5-Might unit, you have a 5-Might copy that's currently sitting at 10 Might, and it drops back to 5 when the +5 expires at end of turn. Attached gear's Might bonus on the equipped unit also still applies.

One caveat: this only works if the +5 is on the unit receiving the Spectacles. If it's the copied unit that's big only because of a temporary buff or its own gear, none of that transfers — the copy takes printed/copied traits only (FAQ #12291).