Again. 2 different issues, I think.
I don't think it's seriously doubted that Wenger's gamble with a development team has not really worked out (albeit that this is a relative concept - given that it has at least kept us in CL football, unlike some of our bigger spending peers). It seems self-evident that in hindsight we have overpaid players who have failed to deliver, and this has hurt us by leaving them difficult to shift, and using up our cash resources.
But I'm not so sure the answer is as simple as many on here seem to think. Bottom line is that the only world class players we have had for 5 years have been development players. Unknowns or kids that the manager has seen potential in and developed. Players that in many cases we have had to reward relatively richly to come to us rather than our more illustrious competitors. We might all agree that we have gone too top heavy on prospects rather than the so-called proven talent, but it seems to me ironic that on the one hand some lament the departures of players like Hleb; Adebayor; Toure; Cesc; Na$ri; RVP and Song, but on the other forget that all of these players were completely, or relatively unknown when they arrived.
And lets fact it - we cannot afford an Aguero; a Silva; a Torres or a Mata with the competition there is out there - and couldnlt do so even if we did not have, say, 4 or 5 of the players whom we now can't shift. Sure, you can buy the likes of Arteta - but he is a very good player, not a world class one. Some of the players we have developed have been world class - and its basically the only way we can have world class players in our team these days. It seems churlish to criticise completely the system that has resulted in this.
Next - I'm not sure our want away problem is to do with planning/timing. What do people want the club to do? Reward players who become want away before they have proven themselves; or cut off their noses to spite their faces by 'getting in first' to flog them before they make Van Persie type announcements. We would like to keep Walcott, sure, but has he really done sufficient to justify a large price tag? Should he be keeping Oxlade on the bench? What should the club do? The fact is that football is player and agent led these days. You either have deep enough pockets to buy loyalty, or you do your best to keep your best assets, but are basically beholden to them - more so once they start performing.
A catch 22 IMO.