I think I'll take a neutral position on the Glazers atm, while acknowledging we have spent less than we might have in recent years - possibly a bit of an ''OK while we're winning'' perspective but you could also say a winning team doesn't require massive investment or need disrupting. So 50/50 there. But also leading to problems when numbers of key players decline/leave simultaneously.
But I feel that there are other pieces of the jigsaw to consider
1) SAF short-termism as he moves towards retirement - Berbatov & RVP, and Valencia even - these being 3 proven performers who did enough in varying ways of maintaining the status quo where Utd = Champions or very serious contenders
2) Clear Fail in the ''buying for the future policy'' or at very least key positions in the hands of potentially good players but we don't really know. The origin of this policy we are not clear about but it clearly hasn't worked as we sit here now.
2a) Someone mentioned complacency a while back - 3 Champs Lge Finals in 4 years was it? Tough to improve on that unless you're Barcelona with Messi
3) Moyes - complete waste of a year, Shaw and Herrera are 12mnths late arriving
3a) Woodward - similar timewasting to 3 and also may be useless/probably is useless
4) Poor buys - add Fellaini & Zaha to this list and there's not a lot of success apart from the 3 proven performers prev mentioned. Kagawa, Hernandez, Young, Nani, Anderson, Jones, Smalling should be big players by now if continuity was going to be sustained.
And here's that list again. The last half is patchy at best and illustrates how/why we are here in my view.
http://www.barriesview.com/2013/05/sir-alex-fergusons-104-manchester-united-transfers
5) None of the more speculative purchases have come in, either - compared say to OGS and going way back Andrei Kanschelskis & Schmeichel even - perhaps our scouting edge has been eroded, everybody knows everybody these days.
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6) As has been said, no one ever seems to leave do they, so we accumulate players that other clubs seem to move on/loan out, and now we've managed to have too many of variable quality in some areas and simply not enough numbers elsewhere. Anything other than 'healthy competition for places' in other words.