Well, I think in years to come looking back, we will be glad that proper time was spent in planning. It may have been a long time coming, but better that than a flimsy business plan and a sub-standard stadium, which the media would have had a field-day with when it opened.
Although the overall spend is huge, remember this is a HUGE stadium with a lot more capacity and facilities than others of a similar nature around the world. I'm sure that the "cost per seat" of Wembley works out to be very similar to that of Stade de France and the Sydney Olympic stadium....