I would hazard a guess that the 'rate' is probably lower now than it was 'back in the day' because radar is better so you're less apt to hit unexpected turbulence. Way back when, I remember hearing that most cabin crew suffered lost work days due to injuries from unexpected turbulence. Something I rarely hear of nowdays.
That being said, there are a lot more flights today than 40 years ago, so the number of incidents may be the same or higher - and of course now we're more apt to hear about it.