I disagree, as I don't think winning in Celtic enhances a reputation one iota in England or anywhere else. We only have to look at Lennon who won 3 league titles and was rumoured to be interested in taking charge of newly relegated Norwich. I think what people wrongly assume is that managing Celtic (or as was Rangers) is a safe bet and a good way of enhancing your reputation but I think what happens is the opposite. O'Neill went to Celtic in 2000 at the time being spoken about as the next manager of many top clubs in England, even Fergie's successor. He won 7 major honours in 5 years up there and nobody in England gave a shit. In fact he returned with his reputation significantly lower than when he left and he was appointed manager of a side that finished just two places off the drop.
Or look at Walter Smith, won 21 major honours as manager of Rangers and in England he took over a side that avoided relegation by goal difference.
I don't mean to sound harsh but I don't think winning titles in Scotland does anyone any favours in terms of wanting to get a job in England or elsewhere. Holland, France, Portugal, etc, are much more likely to be step-ups to the big leagues.