Important, no. Advantageous, yes - but not if it adversely affects operations.stumpjumper wrote: Do you think it's important to have all the bus and rail termini together?
The advantage comes from making the terminals easier to get to and from. But the proportion of long distance passengers changing to other long distance modes are likely to be very small - though still much bigger than the ratio of long distance passengers to total passengers.
Have you been to Brisbane? The long distance buses go from Roma Street station, as do the trains. It's on their busway route, and there are many buses along Roma Street itself. But there are also many routes that don't go there. It's not worth diverting every route to cater to a small minority.
Now regarding Adelaide's local transport network, it's not as ad hoc as you might think. All local bus routes serve either Adelaide Station, Grenfell Street or Victoria Square. My planned underground railway serves Adelaide Station, Grenfell Street, Victoria Square and the interstate train terminal at Keswick, in addition to directly linking the northern and southern suburbs and enabling the regeneration of the SW section of the City. Admittedly some of the buses would be on the other side of Victoria Square from the station, but that shouldn't be a problem, and there's even the option of constructing underground passageways.
So my planned underground railway (unlike the others suggested here and on the poll thread) would directly connect with everything except the airport and the bus station - and the latter could be moved if demand justifies it.