I'm not ready to write off our latest round as poor, but if we look at the last 10 years, and particularly the 6 years since Ronaldo left, I think we can see 3 separate phases, all of which have contributed to our dodgy transfer dealings.
The first, and the one which has been discussed to death, is the Fergie value/thrifty era. During his last years in charge, Fergie seemed to be put off by the ridiculous transfer fees being paid for players who, in his eyes, had done nothing to justify them. Some may argue that the Glazers were pressuring him to keep spending under control, but whatever the reason, we clearly were reluctant to match the spending of teams like Chelsea and City. While I can sympathize with Fergie's disdain for this kind of free-spending, and particularly the role of agents in it, this thriftiness likely led to some underwhelming punts on the likes of Bebe (although you could argue we overspent on him,) Obertan and Powell, while missing out on the likes of Lucas, Hazard and no doubt many others who would've have loved to join United. Somewhat bizarrely, however, Fergie did open the pursestrings for players like Young and Jones, spending the kind of money that may have been better spent on others. It's hard to really pin down the method to our spending madness during this era, but it's pretty clear that our transfer dealings during Fergie's final years were below average (the failure to properly reinvest the Ronaldo windfall being particularly galling.)
The second phase is the Moyes one. Again, it's hard to know just how constrained spending was by ownership (the Fabregas saga didn't exactly put us in a positive light in this matter,) but whatever the case, Moyes and/or Woodward utterly failed during his first transfer window. Bringing in only Fellaini, at an inflated price no less, while failing to strengthen the midfield was a major howler on the part of management. One also gets the feeling that Moyes' hesitancy played a big role (not going all in for Thiago for example.) The reasons for this round of failure may well have been the same as during the Fergie phase described above, but Moyes and Woodward were nowhere the same class as Fergie and Gill at playing the PR game (ie. 'no value in the market.') Instead, they indulged in half-baked split bids and seemed as mystified as everyone else by the Herrera affair.
Finally, we have the Van Gaal phase, one in which Woodward has played a much more obvious and leading role. As I said, I'm not ready to write off these latest transfers, but they certainly smack of Woodward looking to make statement signings, even if they are not ones desired by the manager. Unlike the previous phase, in which caution seemed a byword for transfer dealings, this latest phase seems to have thrown caution to the wind (a necessary step perhaps, given the squad shock therapy required after the Moyes debacle.) Unfortunately, there is still the lingering feeling that we haven't really addressed a number of the issues that have dogged since Fergie's final years (ie. sorting out the midfield and stabilizing the defence.)
Actually, I don't know what the hell I'm on about here, other than to say that we haven't been very good in the transfer market since the heyday of signing Evra, Vidic and later, Carrick.