you've got a short memory... he's won quite a lot.. he's the only
manager who went through a season without a loss...
his insistence on financial prudence is his strength and his
weakness..
I think you have been mistaken. I think the reason Wenger was
retained is because of his ability to generate income. He has a
master's degree in Economics from Strasbourg University. 
I think why Wenger refused to spend big is because whenever he
spent big : Francis Jeffers (2001 from Everton for £8 million -
making him one of the club's most expensive signings at that
point), Jose Antonio Reyes (2003 from Sevilla for £10.5 million
negotiated with top ups, depending on the success of Arsenal, which
could have risen to £17 million.) they all turn up to be big time
failures.
In his 14 years of tenture, these are the trophies he won:
He did win the 2003-04 Premier League
title in 2004 without a single loss but this is it. That is
probably the climax of his career as you all can see that it's
going downhill ever since then. This is the 5th straight season
Arsenal is going home empty handed.