I totally agree. It is not only a need, it is often literally game braking. More then once I had a crash to desktop when I tried to replace a deleted station by a bigger one. So, a simple upgrade button with platform and track expansion is very welcome. (And I like to see also other upgrade tot the station to convince people to use the train, like a parking lot,…)
However, if the space needed for the expansion of the station is taken by roads and all kinds of buildings, it is logical that the player needs to clear the planned expansion space, as it is in the real world: buy and bulldoze the neighbouring houses, and expand the station.