If your considering the SB option then I would say that you need to knock down the Selenity stand and build a replacement that goes the full length of the pitch.The other 3 stands can remain as they are.What we are lacking at the moment is a big shortage of exec.boxes and other corporate facilities.These need to be incorporated into the new stand.I don't go with the idea of a large increase in capacity-15k is too much and I think 12k - 12.5 K is more feasible.
I do think we are punching above our weight when you look at the attendance in relation to the population,so one needs to be cautious about acheiving large increases in attendancies from our current level.
I think we can get away with Sincil Bank's capacity hovering around 10,000 for a while - average gates this season still give us some headroom, although promotion would probably gobble that up.
But any major reduction in capacity during a rebuilding phase would need to be carefully managed - off the top of my head if we knock down / refurbish the St Andrews, we would basically have space left for current season ticket holders, perhaps a few hundred non-season tickets and the away allocation. That would hurt.
I reckon they'd need to look at ways to increase capacity before anything is actually knocked down / rendered unusable. That would mean converting the railway end to standing (which would add 500-1,000 spaces) and/or adding a temporary block next to the St Andrews.
There is of course the option of extending the St Andrews, which if I recall from previous discussions on here was designed with that in mind.
As for knocking things down, I'd look at the most achievable gains with the least impact - the South Park stand doesn't have much capacity and there is space to extend behind. Replacing with a new stand of say 2,500 standing / seats + exec boxes would probably be the easiest significant initial measure, but it would be costly and the current exec boxes would be lost during construction. After that's done, however, we'd have a little room to manoeuvre on upgrading the railway end and the St Andrews.
Bit of a nightmare, but I think it would be worth it.