I think it is not only heatsink design but the overall fixture design as well. Convection cooling can work if the heatsink is open to the air and visible. if you want to enclose it in a housing then you need fans to help move air. And even if open to the air fans will help keep the LEDs cooler than convection cooling alone.
My fixture is enclosed in a housing and I am running 3 low RPM computer fans. I cannot hear the fans at all (well maybe if I put my ear right next to them) and my heatsink is very cool. So I expect very long life out of my array with no noise. The fans should last as they are low rpm thus putting low stress on the bearings and are on top of a closed housing. Unless the location of your aquarium is excessively humid or you frequently splash water up and over your light fixtures I don't see fan reliability being a huge problem.
If you look at the Solaris fixtures that suffered LED failures it was not likely due to the fans but to the fact that there were no real heatsinks to help draw heat away. The heatsink setup of the Solaris units was completely inadequate and I do not think it is representative of what should and could be done with LEDs.
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