we were at Iquacu in Oct 2008 and stayed on the Brazil side for 2 nights (which seemed like plenty of time) in the Cataratas Hotel which is right at the falls - and about the same price as the Sheraton. we had a guide from Blumer travel agency who said our prompt border crossing to the Argentine side (still forms to fill and fees to pay) was facilitated by his company president's organization of soccer games and barbercues with the Argentine immigration military personnel - this is to say that you may have trouble getting across in a reasonable amount of time early in the morning.
as i recall, the tour buses from the Brazil side didn't show up in the parking lot at our hotel on the Brazil side of the falls until about 9 AM after i had finished morning photography. all of which is to say if you want to get morning light on both sides, you should probably stay on both sides and arrange for a morning taxi to the falls if you don't stay at the expensive hotels. the complexity of the falls means you are shooting from many directions on both sides. it was our opinion that the views of the Argentine falls from the Brazil side were better than vice versa (but i believe that trails on the Argentine side were being improved so that may have changed).
a tripod is okay, but there are areas with lots of spray where you really want a poncho and an optech rain sleeve or equivalent for the camera - it also rained like hell for a while when we were on the Argentine side and the Sheraton was happy to provide us towels when we had lunch there. don't recall mosquitos being an issue but that may vary with the weather. some nice birds around in the mornings and a bird park/zoo on the Brazil side
we're going to Buenos Aires, Santiago, and Patagonia in Feb - any advice on Ushia, Calafate, etc. appreciate.