My experience/knowledge of Ashgrove rugby goes back to 1972, and whilst there has been some great improvement from schools like Pats, and the emergence of Eddies and Padua, there can be little doubt that in rugby terms Ashgrove has never been weaker than it is now (although as a school I think it's better than ever).
It's impossible to be certain, but I am confident that most Ashgrove First XV's from say 1975 -1998 would be at least 20-30 points better than sides from the past 5 years or so. I think there are a few reasons for the decline, with one of them being that as the AIC comp is so much weaker nowadays than GPS (with the advent of aggressive recruiting across the board in GPS), and as Ashgrove has won so many premierships over the years, there is no great "glory" per se in winning the comp, and for Ashgrove less incentive than everyone else to build/develop teams to do it (that's not being condescending, it's simply a fact as SLC has been the only other regular winner over the 40 years I have been watching).
Crowd numbers at First XV games reflect this trend as well.
Having said that, I'm sure the individual Ashgrove players/coaches are busting their guts to win each year, and it's by no means a bad thing that premierships are being shared around as the likes of Eddies come through and schools like Villa in 2010 and Peters this year produce their best sides in decades.
For what it's worth, and without giving it too much thought, the best Ashgrove sides I have seen over the years in chronological order would probably be 1975, 1976 ,1979, 1981, 1990 and 1998 (I've probably missed a few good sides in the late 80's) - this tends to illustrate the point I was trying to make above.