Sure, Montevideo and environs would be worth a few days.

You can walk or taxi cheaply around the real old town area and the newer old town. The plazas and architectural styles are interesting. The hotels (and everything else) are very cheaply priced since the economy is in a bad state. The people are very friendly.

You can take a bus tour to head out to the beaches toward Punta del Este. I didn't think the beaches were worth it from a layin-in-the-sand standpoint, but it is interesting to see the sights there and along the way. Colonia de Sacramento is a good day trip by boat from either MVD or EZE.