Top post mate!
Essentially the board cannot force wenger to spend a specific amount of money on any player because his valuation of the player in terms of cost and how important they will be to the team ultimately trumps all.
So, without a football man like DD in the picture, no-one can get wenger to reconsider paying "over-the-odds" for any given player, however absolutely necessary that signing for a specific position must be!
Hence the reason why wenger will dismiss any concerns about his sqaud going into a season by saying he knows what he is doing, he will do it his way, and my personal favorite "judge me in May".
The board, rightly or wrongly have ceded such authority to him because, after all, he is our most successful manager!
But at what point and at what cost will this be allowed to continue.