Most Dominica operators (to my knowledge, unless it's changed since the wife and I were there in 2008) will only do 2 to 4 dives a day, with 3 being more typical (2 in the a.m., one afternoon, although you can arrange for 2 tank afternoon trips and/or an afternoon and evening dive). BUT on top of that a couple of the operations do have a 'house reef' that is usually open as long as the sun is up. My guess is, hunting for macro subjects, that might be your best bet as you can go back repeatedly. Of course that depends on your buddy's tolerance for just hanging out.... But the guides we have were able to find seahorses and knew where all the frogfish were 'rooted' as well, so if you're after small macro subjects they are there on the actual divesites, and the coral cover and sponge growth is pretty impressive. In fact if Dominica diving seemed lacking in anything to me, it was large schools of fish, although we did see a couple we weren't really surrounded very often.
We dove with the Anchorage hotel's dive op, and although I only did the shore dive once, I kind of regret not doing it more. Once we go there "island time" sort of took over and we ended up either skipping a lot of afternoon dives and not doing the shore dive either, the rum was calling. 
It's actually right off their dock, a mostly boulder-strewn and sandy slope down to where the real reef starts, and is actually pretty well covered. Lots of grass eels and the like too in the sandy patches. Extends along the Anchorage shoreline down toward Dive Dominica and the Evergreen hotel as well (and probably well past; we didn't go much further down than Evergreen's dock).
Then further south there's a lot of puffers that hang around near the warmer waters of Champagne (much of which is easily snorkeling depth) where the volcanic bubbles come up.
Nature Island dive to the extreme south is actually right in the preserve, and might be an even better bet as an operation - they've only got smaller boats and are really geared for very personal service so there's a high likelihood you could arrange to be the only pair diving. I've only met Simon once (at a conference - DEMA in FL in 2009) but he seemed a great chap, and it was a good friend of his, Izzy, who helped make my trip such fun. Dive Dominica operated out of Evergreen and also I think took on the divers from the nicer hotel up in town (Ft whatever?), but we did meet some divers on our way back who stayed at the Ev and said that they kept them pretty well separated. Also I think there's a newer dive operation down there as well run by a guy named Woody, who was our surface guide - drove us all the way around the island and took us to some dang nice spots - when we were there. My wife still chitchats with him on Facebook. Wonder if I should be jealous? 
Don't forget the surface options too - lots to photograph in Dominica topside. I've got some pics (not claiming anything special, just some pics) on my flickr site, and there's a trip report up at Scubaboard from before I decided to ditch that site (didn't feel like retyping it all here). Same username there as here so if you search for threads started by rtrski and Dominica it should pop up.
I have not been to Bonaire myself so I can't really compare, but my impression is that a Buddy dive type trip is probably cheaper with more actual diving possibility, aside from the previously mentioned shore dive. At Bonaire you have the full flexibility of site and timing. Of course how much you really do depends on yourself and your buddy, once you're there. Bonaire is on my list as well to go to, but I actually think we're going to plan another Dominica trip first - the wife really liked the topside options there, and if I can find a local buddy (hint hint Izz, if you're reading this) I can dive my brains out 4-5 dives a day while she takes a break in the afternoons to go get massaged or whatever.
I went there 2006 and 2009 , one week each trip . I suggest that you contact my friend Ebby Jules he's a great guide who dives eeeevery day and knows where all the critters are located . I can give you his e-mail and cel phone later ..jpg.857dbbfbdc4d79d9c6ebf7b4ba96ed1b.jpg)
