He can strike if he needs to strike, but it's not the best aspect of his game. All fighters have something they are better/ worse at. I'm sure GSP knows that this is the most deficient area of his aresenal. He has two options--- Step up his striking, or continue to dominate in all other areas to the point that he doesn't have to rely on his striking.
Either way, I dont see him losing another fight at WW. If he does move up to 185, he will 110% have to step up his strikes. GSP probably wont be able to muscle around guys like Sonnen, Marquadt, Silva, Anderson,etc.
I would love to see GSP at 185 against Bisping. That's one dude that I think GSP could destroy even if he fought at 170 and Bisping fought at 185.