Let the grizzles begin.
Already those beyond Noarlunga Centre who think they "own" the line are complaining about the lack of expresses.
The line wouldn't be there if my father and many like him post war had not used it to commute to the city from places like Hove, Warradale, Brighton and Seacliff back in the 50s.
A semi express service would be possible interleaving a stops all on an 8 trains per hour service. It is a moot point whether the time saved on one trip compensates for time lost waiting for another semi express. If you just missed the express would you wait 3 minutes to catch a stops all or 15 minutes for an express and still get to ARS 3 minutes later than the stops all?
You are correct in asserting that removing service from an area is not good.
That is a point in favour of semi-fast trains and stoppers though, not one in favour of a skip-stop "service" which could only be loved by a transport bureaucrat who doesn't actually use the train. Four semi-fasts an hour would provide exactly the same benefits as the skip-stop timetable (increased service to a handful of selected stations) while the four stoppers per hour would provide an even better service to all the other stations - you would get the same frequency but it would be predictable (and therefore more reliable) and the need to use two trains to travel two stops would evaporate.
Semi-fast trains stopping at both Seafords, Noarlunga, both Hallett Coves, Oaklands, Showgrounds and Adelaide which would overtake the stopper at Brighton
would provide a real advantage compared to a 'simple' interleave with no overtaking. Once Tonsley reopens with two trains per hour in the peaks, the Seaford stoppers could run Adelaide-Showgrounds-Woodlands-stops.
The fact remains that, prior to the shutdowns a few years ago, the fast and semi-fast trains on the Noarlunga line were packed every day of the week.
Hopefully this won't be the final timetable, does low-patronage stations like Mile End deserve a 15-minute service during & between the 2 peaks?
Mile End has a number of major peak time trip generators quite close to the station - namely Temple Christian College, Adelaide High School and St George College. Under pre-2009 timetables these students would be required to catch a bus or a train in the reverse direction for the leg between school and ARS - this arrangement was absurd because (a) it was a load of crap and (b) it had the effect of encouraging car use for inner city students with a train station right on the school's doorstep!
Providing a reliable service to these schools is of strategic importance to the public transport system - show students that public transport can be good when they are young and you will maximise the chance that they'll be open to using public transport when they are adults.