You have a good point with this. Playing pathfinder I have come to absolutely adore their version of goblins. Not because they're crunched any different than the standard 3.5 goblin, but because they gave them personality (hating horses and dogs, a fascination with fire, short attention spans, ect.) that really turned them into something awesome (not to mention to wicked artwork).

I think this is good advice for GMing in general. How do you turn encounters from being mundane to memorable? Have some fluff. Why is this monster here? what is it doing when the party sees it? How does it react to the party? How has it affected its environment? Details like that are awesome and really lend to something breathing in the world.

I propose a counter argument however. Is it possible that these heavy-fluff monsters are heavily fluffed BECAUSE they are popular and not the other way around?