I've done lots of trips and never needed a larger passport, lots of countries will just stamp on the same page as the previous exit stamp, though for example if you go to Hong Kong, and then to Macau and into China itself then back to Hong Kong via Macau that will eat up 3 pages so for safety's sake and seeing as it's only 30e I'd go for the larger passport.
Reason being, if you do end up running out of space and need a new passport it will cost you a lot more than 30e in phonecalls, hassles etc when you could be quite some distance from the nearest Irish Embassy.