Bigger is better!.... one word LOMU!..... Of coarse its not the primary aspect to a players abilities but size does give players an advantage. Id say strength is one of the best atributes for a forward (which is why Reid is so good, he's as strong as his larger opponents).
But I dont think that Lomu, or more recently SBW would have had the same impact on the game if it wasnt for there size. Its pretty simple, its harder to push something that weighs more! (which is very handy at scrums, rucks n mauls). Add strength, speed, and some decent offloading skills and u got urself Palu a pretty damn good number 8.
There is no question that Palu is a good player, But i guess a better question is.... is he playing below his weight? Should he be stronger for his size? Instead of being a good player could he be a great player?
It does frustrate the hell out of me when big players play below their weight, eg Chislomn. They have the weight advantage and dont use it.. what a waste.