Before the Cancun trip I want to hit the Flower Gardens again multiple times. The flower gardens are a great spot for macro but it is one of those areas that I think is inevitable for Mr. Big?? to show up and make you wish for a wide angle. But what do you do with that wide angle if nothing shows? When we hit the oil rigs there are plenty of opportunities to shot wide or macro as the structure itself makes for some fun shots. Wide angle at the Flower Gardens and Stetson Bank do not offer as much wide angle interest to me until something decent swims by.
I've been to the Flower Gardens several times and have fifty or so dives there and there has always been multiple chances for wide and macro. "Mr. Big" usually shows a little before and around coral spawning time (but of course when he showed up for 3 hours circling under our boat I was doing survey diving and didn't have a camera......
) Plus I've seen manta at the East Bank or Stetson every time I've gone. Lots of chances for wide. You might just want to go for it! What you do if "nothing shows" is meter the water, have your plan, rehearse and be ready!!!!!!!!
But there is great macro stuff there too. Those tiny chestnut morays are rare everywhere else but are not uncommon at the W Bank and they make great photos (look very "fierce)!
I tried to learn shooting macro with the d200 but it was manatee season here......., so my first hundreds of pictures with the setup were Nikon 16mm/d200, strobes or no strobes. I found the 16mm VERY easy to use. It was equally exposing the bright sky and blue/green shallow spring water that I found challenging. Or lighting the CFWA shots that I kept making mistakes on. But I think I did pretty well for my first outings......
BUT then, as far as you shooting on the platforms in the gulf, I've always wanted a really close up tessellated blenny, you know they have scads of those on the platforms if it is a clear day. I have a good one but I want a great one and with your 105 with a teleconverter or wet-diopter, well you could just stay shallow (IF it is calm......., ha ha)....., but if it was just stay shallow and spend the whole dive on tessellateds, you will learn the 105. Of course when you do that a whale shark will swim by - but hey, all is fair....... 
So I guess my advice is decided what you REALLY want to shoot, what creature you really want pictures of, etc. And learn the lenses for that. Frankly I've taken down my 105vr in the new Subal Port a couple of times and I don't find the 105vr any more difficult than the 60mm, but I had no experience with the 60 either, so I think you are good to pick up just about whatever lens you want to learn on - you have no "pre-concieved" experiences with DSLR and like me you will have to learn anyway, learn on a lens that will let you shoot what you want to shoot.
My take on it from a gal, learning her first DSLR since December 06.
Best, Carol