I've been to Malta a couple of times and found it to be a *very* enjoyable country. Valletta is a very memorable city, especially if you turn off the main tourist strip and wander through the precipitous little side streets, but in many ways I think the Three Cities (Senglea/Cospicua/Vittoriosa) on the other side of the Grand Harbour are more visually striking.
Even if church interiors aren't your thing, St John's Co-Cathedral (where you'd be anyway for the Caravaggios in the oratory) is incredible; I'm not generally a big fan of the sensory overload in Baroque cathedrals, but this one is successful at doing complexity without exploding into a visual mishmash. I'm confident there are a lot of interesting photographs in there waiting to be taken. (Cameras are OK, flash is not.)
Note that they will not let you photograph the Caravaggios! But I expect you knew that.
But I think the island is more interesting outside of Valletta (and of St Julians, which is just awful, a crowded holiday strip full of drunken tourists). The people are quite approachable, once you get out of the tourist orbit of jaded shopkeepers and so on, and there's a living agrarian culture that's quite unusual in Europe. This is even more true on Gozo, which is a largely rural island covered with terraced agriculture, some of it still worked by hand. I'm horribly inept at approaching strangers socially, but someone more skilled could have a great time doing portraiture out in the "real" Malta.
The island is so small that you can stay pretty much anywhere and get around using the bus system (which itself is not to be missed; you could do an entire project of portraits of Maltese bus drivers and their vehicles). The only place I've stayed that wasn't a business hotel is the San Antonio Hotel & Spa in St Paul's Bay. It was eccentric but lacked any serious problems, and was extremely cheap in the off-season.
I've never been there with a really startling camera, but in my experience the place is entirely photo-friendly; they're used to tourists. Certainly setting up a tripod is a perfectly normal activity; a view camera might attract attention, but of a benevolent kind. But I would suggest taking a rollfilm camera as well, simply because there's so darn much to photograph. (I'm not sure that the Co-Cathedral would let a view camera in; you might end up in one of those strange arguments about whether you were a professional who needed special permission.)
There are regular fast ferries from Sicily, but I think they only run a couple of times a week; make sure of your schedule beforehand if that's how you're getting there.
Sorry for the braindump. I get like this about places I like.
-NT
