The train services to and within Cornwall are as bad as the bus services anyway Bruce.
The train journey to St Ives is honestly one of the most scenic in the world. But it is literally a 4 stop route that takes about 10/15 minutes. So I don't think Cornwall's rail service is effected by this at all. Oh, I think Falmouth Town centre station is also closed for some reason, but there are 2 other stations in Falmouth.
TBH, the media are trying to portray an image of the locals being massively disrupted by the G7 conference, and for the residents on Carbis Bay itself it probably is a pain in the arse. But Carbis Bay is only a small village on the outskirts of St Ives. which is open as usual albeit the main route into the town is closed, which means the other routes (minor country roads) will be a lot busier. But St Ives is used to this. You can't get near the place in the school holiday period and the locals will have known much worse than this disruption.
The vast majority of Cornwall is in favour of holding the G7 summit as it showcases the area to the world. There is also a lot of ecological things going on down here and the county is looking forward to promoting this. There's even been a couple of ecological songs written and performed by children that will be played to the G7, one by Tim Rice and another, which doesn't mince words in the lyrics, sponsored by the council. The latter, called Hey Human, 7 songs for G7, is quite hard hitting and I recommend people google and watch it.
Bottom line is that the disruption will be for about 10 days, but the legacy of holding it in Cornwall will hopefully make it worthwhile.