What's the semantic difference between "overrated" and "overvalued"?

Solution 1:

Overrated means that people hold it in higher esteem than they ought to. Overrated implies that people have a (too) high opinion.

Overvalued means that people place too high a monetary value on the thing in question. They may over value it because they overrate it, but the converse is not necessarily true.

In the case of the expression "overrated and overvalued" I suspect that there is a possiblity that it is being used for emphasis, but one would have to see it in context to see whether a literal interpretation is apt or whether it should be taken more figuratively.

Solution 2:

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.

EDIT: 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)