I hear that a lot but I guess it depends on how you view + plays in forming your opinion.
At worst, a + play prevents an extra base.
At best, a + play turns a hit into an out.
If you add 30 bases to a hitter's numbers, his slugging goes up .060 based on 500 AB. In my mind, that's pretty significant. If you consider them hits, you've turned a .300 hitter into a .360 hitter with the appropriate increases in OBP/SLG. In turn, take hits/total bases away from those COF and they're not quite the same either. I won't even bother to get into the effect +/- have on a pitching staff.