my friend, Cartagena is declared patrimony of humanity by the UNESCO. Land is very expensive, yes ! It is the most expensive city in Colombia. However, it does not have Hurricanes like Miami, nor shark attacks. In other words, if you live in Miami, you might have to build your house more than once , of course, hoping that you survived the hurricane or that a shark didn't eat you.
I agree the beach is not the best...., but I can tell you didn't go to Baru island or the north side of Cartagena, where the beaches are nicer than in Miami. I can also tell you have not traveled much around the world. You may find people harassing you in every single place that bases its economy in tourism. It is part of traveling.
All in all, you need more than two weeks and an open mind in order to really appreciate where ever you go.
I do hope you go back one day !!