For a UK E-3 replacement, isn't the process something like this:
Take a perfectly good system, strip out all the electronics to create jobs at home, send BAE gobs of money to integrate a solution, ignore warnings, add/change/delete requirement several times, then scrap or rebuild the entire thing to get you something close to the original perfectly good system? I may have missed a step.
On a serious note, I think a larger platfrom with more consols is always a good way to go if you can afford it. Systems that we never even thought of tend to get added over the long life of these airframes. Yes computers have reduced the workload, but a good platform still needs many brains to process, talk, direct, etc. The E-2 and biz jet designs are just to small to get a capabilty like you get from a E-3.