It turns out that these two are some of the most valuable properties in the game, if you know about an obscure rule of monopoly (often only followed in official tournaments, or when playing with rules lawyers such as myself). Basically, you can buy both of these properties very cheaply, and then build 4 houses on them very cheaply. Then, ideally, you have a couple of more expensive properties, and at least one of the other available monopolies on the same side of the board as baltic/mediterranean (as those can also build houses for $50 a pop). You do NOT want to build hotels (at first) if you are following this strategy. You DO want to be the only player with any properties having 4 houses.

The rule is usually referred to as 'housing shortage' - once the board runs out of houses (there are 32 supplied with the game), no one can build any more houses. And unless they already have 4 houses in place when you run out, they cannot build hotels. You control ALL building improvements. You can retain control of the game by only building hotels when you have space and money to buy back the four houses on the same turn, making it impossible for anyone else to use them (unless they buy them from you, for insanely high prices.)

Then you just sit back and wait to win while your opponents beg and curse at you for mercy (once they've looked it up and are forced to go along with it.)

I have won actual monopoly tournaments using this strategy (well, one.. and several less official games). The problem: it only works once against a given opponent. If are aware of the danger, and you know someone else is trying to cause a housing shortage, you can prevent it by getting four houses of your own somewhere.

So, I heartily agree with the parent poster.