Re: speeding up Gippsland vlines on Pakenham and quadding - it'll probably not pass the pub test at Treasury if it's just about benefits for Gippsland Vline, you have to include Pakenham benefits as well.
Plus, a reversal of thinking may be required - starting from the outside and working in, through two phases.
Starting from the Pakenham end, rather than the city end will provide some benefits - but not all - if the quadding is done Pakenham-Dandenong-Oakleigh as the first phase (in all areas where there's oodles of space on the surface/space left over from the LX programme for more track.
From the city, everything would have the same stopping pattern to Caulfield (Pakenham/Cranbournes via ANZAC / Vlines via SY then express to Caulfield) then Pakenham/Cranbourne SAS to Oakleigh and Vline expresses/limps behind metro and then Pakenham/Vline go onto the new track pair/Cranbourne stays on existing pair. Pakenham/Vline stopping pattern is the same: Clayton for SRL then Dandenong, Cranbourne stopping pattern is SAS to Dandenong. From Dandenong, Pakenham metro uses existing pair, Vline uses new pair. Oakleigh-Dandenong should aim to have max speed of 100kph, Dandenong-Pakenham on new track pair should aim for 130-160kph.
Vline and Pakenham get faster journeys (thanks to the Oakleigh-Clayton-Dandenong express section) and then this allows a second phase to built at a later date like the one in the leaked NDP from 2018 (i.e rather than quadding Oakleigh-Caulfield, a new line that diverts to a station at Chadstone then another track pair - probably underground - between Caulfield and South Yarra).
If we can accept that it'll be slow in the Caulfield-Oakleigh section (or we're happy to terminate Vlines at Oakeligh or Clayton - whether all or some is another question), at least for the time before the second phase is built, you'll see benefits elsewhere... and when it's complete more benefits are unlocked plus potentially new destinations (eg. Chadstone from the NDP).