I'd visit more before making a decision. I've been in Miami nearly 9 years and would love to leave if I could afford it. I teach at FIU, am tenured and the national job market in my field is slim. DH and I are plotting an escape if we can get the finances together, perhaps when our babes (due in June) are a little older.
I just posted an answer to another thread today by a woman asking if it's possible to live holistically in Florida. You might check that out.
I agree with PPs that Miami is very diverse and there are some wonderful attributes. I love the weather, the Everglades and waterways salt, fresh and in-between. We BBQ in the yard year-round and I actually like refreshing my Spanish skills little by little.
However, the property taxes and insurance skyrockets every year. Our mortgage is now nearly $1,000 per month than it was 7 years ago when we bought... If you are well off you might find comfortable places to live, work and play. If not, you'll have to be both creative and tolerant.
And yes, traffic is abysmal. I drive in the opposite direction of Miami's rush hour and still need an hour minimum to travel 10 miles to work.
It's definitely helpful in most areas to speak Spanish especially if you want to get your car fixed, your hair cut, hire a baby sitter or have your plumbing repaired. IME English-speaking services often cost double or triple.
The schools here are generally very bad. As I said, I teach at the state university and find the students incredibly ill-prepared by their public school educations. There are good private schools if you can afford them.
If you like the outdoors the Everglades and many of the state parks are incredible, although they suffer from a great deal of environmental degradation.
Many parts of the city are dangerous in terms of crime. Friends of ours live in Coconut Grove and are constantly suffering break-ins to their home and vehicles. Be wary of nice looking neighborhoods that are bordered by ones that look bad. I don't mean to sound bigoted, but there is great prejudice here and to be poor in Miami is to be terribly disenfranchised.
I'm not as familiar with Little Haiti, though a colleague lived there during her first year in Miami and had a negative experience. Talk more with your relatives, visit if you can. If you come here I'd be happy to meet you. PM me if you'd like to talk more specifically. I don't mean to be entirely negative, but you should feel comfortable with what you're getting into before making a big move. From a selfish point of view I'd love more crunchy folk to move here! Good luck in any case.