Coming to this thread after being at the park yesterday for the first time in 4 years.
The monorail is embarrassing. Dirty, slow and not fit for purpose.
It's such a shame as I remember going to the park for the first time in 1995 as a teenager and having that magic "wow" moment as the monorail went past nemesis. I remember it so vividly now.
That's what cemented Alton Towers as the magical place I hold dear. So many memories.
The initial (and last) experience a guest gets is what frames the day. I think they need this to future-proof the park, even if it costs them a bomb.
I think the decline in the park's polish was when the advertising on rides started (Cadbury's Heroes for air?!) and the decals on the monorail - you could no longer see the rides well through the windows to marvel at the park you're entering.
I'd advocate till I'm blue in the face for them to keep the monorail track / route and get new trains as there are so many new visitors who should have that "wow" moment I had in the 90s to fall in love with theme parks.
Edit: typos