Indeed.
I remember going to watch Leinster play Glasgow Caledonian (as they then were) in a European fixture of some sort in 1999 (I think) at a club ground in or around D4 (Old Wesley's ? You can tell I'm not a Dub ! :) )
Anyways - there were no more than about a thousand at it. At that stage Ulster and Munster were getting decent crowds, but Leinster weren't and Connacht were woefully supported.
About a decade after that Leinster were selling out Lansdowne and the RDS for matches, which shows that things can change.
P.S. I'm not trying to be one of those 'I was in the GPO in 1916' bandwagoners I mentioned above with this story :)