From having used these a few times recently, one thing would be a dedicated fleet of higher powered units, because they always seem to crawl up the bank before Plymouth. Or simply get the wires up! All the way to Penzance would be difficult to justify, but Plymouth you certainly could, even if you had to have a short section of diesel or battery running along Dawlish (though I'm not 100% convinced by this as there's a similar electrified line in Scotland).
This would be an utterly silly idea as several of those are the big origins/destinations! Penzance itself isn't that busy, it's a "local town for local people" with far less tourist traffic than say St Ives.
But it is just as silly to me to be having at least four trains in an hour stopping at those stops that travel between at least Penzance and Plymouth, if not then also travel on to Exeter St Davids to go on to other destinations.
You have the following trains over the next two hours:
2P12 11:15 Penzance to Plymouth using class 802020 stopping at St Erth, Camborne, Redruth, Truro, St Austell, Par, Lostwithel, Bodmin Parkway, Liskeard, St Germans, Saltash, Plymouth
2P13 11:50 Penzance to Plymouth using 110mph pathed castles class 43's 43154 & 43092 stopping at St Erth, Camborne, Redruth, Truro, St Austell, Par, Lostwithel, Bodmin Parkway, Liskeard, Menheniot, St Germans, Saltash, St Brudeaux Ferry Road, Devonport then Plymouth
1A88 12:15 Penzance to London Paddington using 802103 stopping at St Erth, Camborne, Redruth, Truro, St Austell, Par, Lostwithel, Bodmin Parkway, Liskeard, Plymouth, Totnes, Newton Abbot, Exeter St Davids, Tiverton Parkway, Taunton, Castle Cary, Reading then London Paddington
2U24 12:50 Penzance to Plymouth using 150265, then on to Cardiff Central stopping at St Erth, Camborne, Redruth, Truro, St Austell, Par, Lostwithel, Bodmin Parkway, Liskeard, St Germans, Saltash, Plymouth (This service is pathed for class 43 doing 110mph)
2P16 13:15 Penzance to Plymouth using 802010 makes the same stops as 2P12 plus as stop at Hayle.
2p17 13:50 Penzance to Plymouth using 800002 makes the same stops as 2P16.
I agree that Penzance is not a busy station, but times I have been in Cornwall and Devon, St Erth, Camborne, Redruth, Truro, St Austell, Par, Lostwithel, Liskeard, St Germans have not been busy stations either, especially during the day. So why are so many trains stopping at these stations? Surely, you only need the Penzance to Plymouth services stopping at these stations, there is no need for the London paddington and Cardiff Central trains to be stopping?