But Miguel this type of analysis has 2 major flaws.
First it assumes when you compare one seasons spend between clubs that each club starts from the same place. That obviously is not the case. When a club already has a quality deep squad and spends a modest amount for 1 or 2 additional players they are still likely to have a stronger squad, and therefore a stronger chance of success that a club who may have spent significantly but whose squad was rather barren of real quality prior to investment.
Second, this takes into account just one expense, the transfer fee. Now a transfer fee may have some correlation to the quality of the player being purchase, but it also has a strong correlation to the number of years left on a players deal at his existing club. A better and more consistent metric that correlates with a player’s quality is wages, and none of this is discussed here. Case in point Yaya Toure cost City 24M, not cheap, but in the range of ourselves and quite a few other clubs. However he's on 200k a week, which means only a limited number of clubs, would be able to afford his services. But additionally wages would show up for many players who are on loan deals (at least the unsubsidized portion), yet in terms of transfer fee's these players cost nothing. So for instance Spurs have to pay significant wages (even with City subsidizing) for Adebayor’s services, yet your analysis looks like they have him for nothing.
Finding wage tables are a little harder and often out of date as obviously clubs like most businesses are not keen on publishing them unless they have to. But from what I've seen historical data suggests there is a very strong correlation between what a club pays its players, and where they end up ranked in the league table.