Happy Anniversary! Congratulations too on your years of wedded bliss. I wish you many, many more lovely years together.
I don't know Miami well enough to suggest a "regular" place. I can say that if you want a really nice place to stay, check out the lower priced offerings you'll find here:
http://www.thetopvillas.com/miami/. I've rented booked with them for several vacations. They've been quite accommodating, everything from maid service, cooks, transportation, you name it.
Surprisingly, the cost (at the low end) is comparable to a high-end hotel, but what you get in return blows places like the Ritz or Four Seasons out of the water. Take a look at this property:
http://www.thetopvillas.com/miami-41/ . For ~$3200-$4000 (~$500-$600/night) for a week, look at what you get.
If you want something that's one block off the beach (across the street from Heritage Park -- they may even have a free outdoor concert while you are there), check out this flat:
http://www.thetopvillas.com/miami-36/ .
I'm not at all suggesting that it's inexpensive; ~3800/week isn't. There are less pricey places to stay. By all means, if you don't want to do the "luxury thing" on your trip, you can have a perfectly good time nonetheless. It's your anniversary and the company not the accommodations is going to make it wonderful.
Of course Top Villas aren't the only service of their kind; they're just one I'm familiar with and have found to have what I was looking for on a few occasions. I don't have a reason to prefer one over another; it just depends on who has a property available where I want one on the dates I want it.
Sometimes booking a vacation apartment/house leaves one entirely on one's own in a strange place, and that can be daunting, particularly where one doesn't speak the language (or speak it well). That isn't going to be so in Miami for you, but even so, getting good "411" on where to go, along with having a local (usually the cook and/or the driver if you arrange for them) on hand for "whatever" is a blessing.
I especially like having a local cook or driver because unlike the "concierges" at hotels (or even with the vacation rental services), cooks and drivers don't presume I want to spend "an arm and a leg" on everything every time I want something. I'm never disappointed with the input I get when I ask them, "Where would you go if you wanted....?" I can't tell you how often questions like that have landed me in the most charming restaurants and/or bars and clubs, interesting places to visit that I'd never have found on my own, quaint little boutiques, even just nice places to hang out or take a stroll.
Well, anyway, that's my suggestion. Make of it what you will. I'm sure you'll have a lovely trip whatever you do, and no matter where you stay.
All the best.