Personally, I think that when T5 is finished, they should move the T1 and T2 traffic over there, knock down T1 and T2 and re-build them, then once that is completed do the same with T3. I know that this would take a long time, but it's one of the only real practical ways of getting rid of the old terminals once and for all.
If the builders were employed to work on it 24-7-365, then it could be completed in next to no-time, but the way things are built here in the UK, it seems that workmen only work half days, here and there, so things take years to be completed.
Another alternative that my manager actually proposed to the BAA was to pull down all the car parks in the central area, demolish the tower (new one is shortly begining construction anyway) and build one huge check-in hall that links all the previous terminals 1,2,3 together, this way it would become kind of like AMS is now, just one huge terminal with satellite piers for the boarding gate areas.
The 3rd runway would slot in nicely between the A4 and the M4, and to save demolishing as many houses etc, if it way made shorter than the present runways it could just be used by short haul a/c. Or how about using the 2 runways that are already there, and operate both of them for simultaneous take-offs and landings. Traffic could be increased with no new runway.
Just my 2p's worth
"She Rolls, 45 knots, 90, 135, nose comes up to 20 degrees, she's airborne - She flies, Concorde Flies"