I really don't see the problem with the use of alpha suffix routes. As Aquavid said, the 46A is the best known route in Dublin, and I would say it's the "A" which makes it that bit more known. I'd put the 10 in second place for best known routes, but the 46A wins hands down, it's almost like a designer label for some folk in Dublin.

Passengers are not confused by an A or B separating the route. I admit when looking at the Dublin Bus routes on paper it does seem confusing. Especially with routes like the 17 and 17A having no connection at all. But people adapt easily to change and generally have no problem understanding the difference between a 15A and 15B. In some cases it would do no harm to have a few more alpha suffix routes. The 42 is a prime example where greater clarity is needed, perhaps something similar for the 84X, but that's another web of confusion.

If proper customer information is provided at stops then it really should not matter how many digits or letters are in the route. Too often do we see big route changes with no bus stop information provided.