2 problems with this though:
1) As already pointed out, the stations at Argyle Street, Partick, Hyndland and others on the North Clyde and Argyle Line routes are not suited to 23m units - the level of ASDO required wouldn't be suitable without extending the platforms which would likely be prohibitive. The more sensible option would be for any new units on these routes to be 20m so as to avoid what would be ultimately unneccessary alteration works.
2) Running more frequent (and possibly shorter) trains are far preferable to running fewer trains. A 15 minute frequency will attract more than double the patronage than a 30 minute frequency. People don't want to have to plan part of their day to be at the station for a certain time to catch a train, so they don't miss it. When we are trying to encourage people away from car usage, a 'turn-up-and-go' service of 15 minute (20 min at a push) frequency within the city at least is what is needed as minimum. Obviously this wont work on certain routes due to single line etc, but what can't happen is to use train lengths to decide that we don't need to have more frequent trains - that's the opposite of what should be happening.