I think 2-3 in the 90's, 2-3 in the 00's and none in the past decade. Might be wrong.
Since 2 or more teams play in the CL, I think mid 90s onwards, they missed it once. In 2007 when Stuttgart won and Schalke and Bremen were 2nd and 3rd. Under current rules however, Bayern would have still qualified since they came in 4th.
Competition and chance of relegation is all nice, but 10/15 of those clubs always make the CL. And a lot of times it will be 12/15 if those permanent members. So these clubs quality anyway, what this does is, it eliminates the possibility of these clubs losing sponsorship and tv money THEY attract (because no one is giving UEFA contracts for the Dinamos or Atalantas, they get the money they get for the Madrids and Bayerns), for one fluke bad season they have, or for one fluke good season of a random Leicester or Udinese. Plus they don't get near as much as they should. So the idea was mainly money driven (same as UEFA), true, but if I do all the work and you get half the money off it, you damn we'll be sure I will try to take it back from you.