Unlike in many sports, equipment really, really matters in golf. It's not that good equipment makes a bad golfer better. It's that good equipment allows a good golfer to really use his skills. Sort of like a fine instrument.
My brother was an All American golfer. He got new irons and shafts before his senior year of college, and had his worst start since sophomore year of high school. Switched back to the old clubs halfway through the season, and right away finished runner up in one of the biggest college tournaments of the year. Apparently the new irons didn't allow him to shape his shots as much as the old ones. It turns out he also needed far stiffer shafts than you can get at most golf shops, because he produced so much power that the shaft would still be way too bent at the moment of impact. The only way he could play with the newer equipment is if he reduced his power, and just accepted the fact that he'd have to shoot straight every time. (Personally, I thought he was an idiot for getting new clubs at the beginning of the season, instead of in the fall, but there you go.)
As for the quality of Nike clubs, I've heard mixed things. It's worth remembering that slight differences matter a great deal at the PGA level, and that it's not just about good club vs. bad club, but rather about whether the club suits the golfer. Also, whether a club is good for a PGA professional has little to do with whether it's good for a recreational golfer. Good recreational clubs have huge sweet spots, but also don't give you the same kind of control over spin that a professional golfer needs.