What is the semantic difference between rate and value?
Rate in the sense used in overrated means "assign a rank or rating to" and value in the sense used in overvalued means "the amount that something is worth, measured especially in money".
The connotations carry over perfectly:
overrated can only be used if someone thinks (says, implies) that something is better (rated higher), compared to what someone else1 thinks about it; also there is an implication that both parties rated it.
overvalued can be used when someone thinks that (says, implies) that something has a higher value compared to what someone else thinks.
Something can be overrated even though the value is the same as the things you compare it to. Also something can be overvalued due to factors that have nothing to do with rating or quality.
1 Normally this "someone else" is taken to be in majority. Using either of these terms is an attempt at objectivity (so often used without real basis in marketing)