It seems I missed this thread the 1st time around.
1. Paisley closed due to a lack of patronage. Their is no real reason to think this will have changed.
2. The pedestrian underpass is filled in. One opening of the underpass has had the Western Standard gauge line built on top of it. A new underpass would need to be built.
3. Paisley is in the wrong spot. If it were on the Altona loop line, or East of the junction then there would be a case for it, but being on the express tracks means it can not be re-opened in its former position. For why an entirely new station in either of these preferred locations see point 1.
Just because it was there in the past and nobody bothered to bulldoze the platforms after it closed, doesn't mean there is a valid case for it re-opening.