You are kind of correct about something happening when clicking on a buoy. Only, the one I'm thinking of is in New Sorpigal. Go to the peasants' camp that's kind of NNE of the Abandoned Temple, and NNW of town. Get as close to it as you can; face the Volcano, and click on the Buoy.
That's really the only one I know of that actually does anything.
On a related note, I've found that items that do something (Hidden treasure, whatever) are either captioned when you hover the cursor over them with Capital Letters (Or not at all,) while ones that are just part of the scenery are captioned with all lower-case letters. Such as "torch" and "Torch" or "tree" and "Tree" .