know that both SA's shrug off Venom, Ram, MR, Polearm, etc- but does this mean that they cancel out ALL 1-click damage? Including if a character attacks successfully, but only deals 1 click of damage? Likewise, does invulnerability cancel out ALL 2-click damage ratings, as well?

Or is there a basic minimum of 1 click for such things?

for Unlimited and Conquest Toughness reduces damage by 1 and Invulnerability by 2, with no lower limit. So as you say they "deflect" Ram, Polearm, Venom and also Shake-off damage (but not push or critical miss.) They also reduce combat damage by those amounts, so a successful attack that does not exceed the "deflected" amount might as well have never been launched.

In Dungeons the reduction of combat damage was to a minimum of 1, but I don't know if that's still the case or if that was changed.

Yikes...

last tournament I played in someone threw a Skeleton on a Creator who chose not to push to break or attack. Next turn the Skellie took a swing, with Weapon Mastery: got the hit, and rolled a two...talk about your let down. The Skellie's controller insisted it was a moral victory...

a skelly going against a creator???
now, that's something to BEHOLD :)