You're right in saying a lot has changed since Kevin Cronin walked those routes back in the mid 1990s, the last ten years in particular has led to a lot of new construction on the former trackbeds.
But there has been some positive developments, for example, much of the North Kerry route has since been developed as the GST, and Newcastle West station has been stored and is nowadays immersed in a new housing estate, unlike its derelict state in 1996.
Newport to Achill has since been restored as The Great Western Greenway. The section of the Aughrim line has also been restored as you mentioned, and the W&SVR nowadays runs trains on the trackbed between Kilmeadan and Waterford on the Dungarvan line.
However, Upton to Waterfall on the CBSCR is no longer walkable due to recent private housing built on the route.
Elsewhere, stations I've discovered have been developed and expanded it fully private residences and nowadays I would see it not possible to simply walk through them. Some routes are also virtually impassable due to the overgrown nature of some trackbeds, for instance it is not so easy to walk the Killeagh section of the Youghal since some track was lifted in the mid 1990s.