Not for the sake of it, no. There are plenty of s*** foreign managers too.
But we have definately suffered since Sir Bobby's dismissal because we've seemingly limited the possible replacements every time to 'British only', at a time when there is arguably only one top class British manager still active in the game and a handful of others who are decent but nothing spectacular (the best probably being O'Neill).
In fact, I would say that we haven't appointed a "foreign" manager since Keegan transformed the club with Sir John Hall's money. Gullitt may be a Dutchman with a funny accent, but his managerial CV at the time we appointed him only had "96-98 Chelsea - 1 FA Cup" on it. So he had never managed abroad prior to that. The main point being that our current and previous chairmen/owners have been all too happy to sit on their arses and make the "easy" appointments, i.e. people that they know or have heard of because they're from, or have managed in, the same country, when the better, more difficult route would have been to use the vast resources at their disposal and get a couple of board members, directors, non-executive directors, high ranking club officials, etc etc, to scour the globe looking for talented managers. Managers who have done well with their resources, are of sound character, have produced good teams with acceptable/attractive tactics and styles of play, blooded talent through consistently, shown a good eye in the transfer market, qualified for continental competitions and done well in them, have a good overall track record, so on and so forth, then appoint the best man according to their findings. Clubs like Chelsea, Liverpool and Arsenal did just that, at a time when we could also have done similar. They're reaping the rewards whilst we're most likely going to be playing in the Championship next season.
Not wanting to get into a Shepherd vs Ashley debate, but if we're talking about managerial recruitment policies, it's worth noting that we were so very lucky that Sir Bobby was a Geordie (or as close to one as you can get). Honestly, a world class manager with a great continental CV, someone who had managed the best in Europe and done well, someone who could be expected to take over an elite club given his track record, was also someone who happened to be a childhood supporter of our club, having grown up in the surrounding area, and willing to come to us to see out his career even though we were near the bottom of the league with no money to spend and a s*** squad overall at that time - just how fortunate were we that we had that? Most clubs aren't, in fact no British club at this point in time has a top continental manager proven in Europe at the highest levels with some sort of emotional tie to their club to the extent that they are willing to manage it.
Take that lucky break away (if Sir Bobby was a Portugese or Spanish man by birth we'd probably have never even considered him), and most likely our woeful managerial selection policies would have come up trumps again in terms of finding the right man to tear the club apart or at the very least ensure that we get served woeful football week in week out without ever improving or looking like we could do so.
