To put that in context the Marston Vale line (excluding Bedford Midland and Bletchley) was 426,900. Bletchley and Bedford's figures combined are just over 5m so if 10% of those are headed for the Marston Vale you're at the same level as the Island Line. From my office window I can see the Marston Vale line - the trains are overwhelmingly empty most of the day - they are carting about fresh air most of the time, so notwithstanding the platform length issue that one doesn't justify more than 2 cars, it's difficult to see how a similar case can be made for the Island Line.
now you just have to figure out WHY it is empty most of the day,and find ways and means to make it not empty.
In the case of marston vale,I believe it's purely down to bad connections.....it is cheaper /faster to use alternative means from bedford-MKC...sort that one out and you will get decent footfall.
I have banged on repeatedly about the need to properly integrate transport hubs..and both bedford and bletchley come up short here. MKC with plusbus would work,but bedford bus connections from the station are useless.
Fact of the matter is MK IS a hub,bletchley IS NOT.Bedford could be,but ISN'T
in the case of island line.I think it's down to seasonal demand obviously,but also lack of truly integrated island(or island with mainland) ticket, and also the council's reluctance to stage other events outside peak tourist season.
A few extra concerts could fix it...even if it means subsidising the site fees/easing planning /noise restictions... you would make the money back on and then some from accommodation/bars/restaurants etc.
also diversify the events...ok you have a bit of horse racing and bestival(..hmm....lets see about the line-up there, is it going to be cutting edge popular stuff or kajagoogoo have just finished playing butlins in minehead and are close by???..only so far you can push re-treads.)...what about making a purpose built music arena, a bit of motorsport, worst case turn ventnor into vegas..complete with poker tournaments,go-go girls and cabaret!!!!