The answer to the poser in question is pretty simple, but it's indeed a million euro question only the Arsenal manager can answer with relevant support from reasonable ideologies, not hasty generalisation based on a rather quick but sentimental approach.
So, I'll try to be as brief and straightforward as I can, while I attempt to answer the seemingly harmless question.
I think Arsene Wenger choose not to pay €8m for Marouane Chamakh, because the player was verbally handed to him (unknowingly), by the President of the Haillan outfit Jean-Louis Triaud. The Bordeaux Chief infamously belittled Sunderland, as well as, other small clubs who at a stage of the negotiations were more than ready to snap the Moroccan international.
Our erudite gaffer might have taken notice of this, instead of doing a Barcelona, he decided to take his time. During this period Arsene calculated Marouane Chamakh's marginal utility and it was good, so he decided to play hide and seek pending his improvement and the result of that fruitful gamble calls for celebration.
So, Wenger's ingenuity came to the fore and he basically bought without paying - simply because there was absolutely no need to pay for a commodity that was already freed from external influence and competitors. The Wenger we know, didn't dissapoint and has taken full advantage of Triaud's help to add the forward to his list of astute youngsters at the Emirates, as he assembles his squad ahead of next season's business.
On why I think Wenger is willing to break his savings box for not just an inexperienced player, but also an unknown quantity, whom soccer analysts in his home country have written off.
Based on this somewhat false misconception, some people believe the Arsenal manager, who is currently putting his monetary skills to work in South Africa has lost his eye for 'spotting the next big star'.
Their arguments can be substantiated, given the rather unfortunate happenings at our five-star talent producing academy. An unforeseen development doesn't mean the boss is done yet! Arsene is arguably the best - the key to our success story over the last 13-years has been the Frenchman's knack for transforming feeble youngsters into confident and mature leaders, and if Wenger succeeds in signing Laurent Koscielny from Lorient this summer - that won't be the first time he's risking his pennies on a hugely inexperienced kid.
He signed far worse players, brought them up via the Arsenal way, sold them as superstars a few years later at quite profitable rates; Patrick Vieira, Thierry Henry, Emmanuel Adebayor, Kolo Toure are all a testimony to that fact.
Before he signed Adebayor from Monaco, I can bet my lunch the Togolese striker was just as wasteful as some claim Chamakh is. But we all know, how many goals the former Arsenal striker scored in just one season to merit a cheeky £25m, or the bitter truth that Arsene paid a meagre sum of £500,000 for current Chelsea forward Nicolas Anelka, whom we happily sold for £22m some years later.
I think Koscielny or any other kid Wenger is interested in should be given the benefit of doubt at least for now - Vermaelen is a tackling evidence, and only a few have actually failed this stern test, most notably Jose A. Reyes, who is currently making the headlines in Spain for Athletico Madrid.
Believe it or not! Arsene Wenger is the best man for any bargain deal, and of course any football team with long term goals as well.