Let's say a character has the Robe of Runes and Spell Focus, and Greater Spell Focus (evocation)
With the feats it's a +2 DC on the saves, but Robe of Runes reads like this. For 1 round after recalling a spell, the wearer's spell save DCs and attack rolls made with spells gain a +2 enhancement bonus.
So a recalled evoc spell's DC would go up by +4, or no?
Yes, these stack. The feats grant untyped bonuses to the save DCs, while the robes grant an enhancement bonus. Together, that stacks.
Good that makes Robe of Runes worth every gold piece then.
Yes they do.