The two events are different though, and at least this year the organisers did try to differentiate the two (different websites for starters). The September festival is the showcase whereas the St Patrick's festival is mainly just for drinking. I would also posit that the March event is for tourists and the September one is for the locals.
If the location was to change from the IFSC to a nicer venue, I doubt the event would get the footfall. Also, I could see another event popping up in its place at Georges Dock.
For myself, I definitely prefer the September event, but then I'm old and I like my luxuries; That being said, I had a cracking night last Friday with a great gang of people (might have been a couple of brewers there too) and some fantastic beer.