IMO we need someone that would attract players to the club - someone that decent players will want to play for. The manager is as much as an attraction to a player as the club profile and the money.
If we continue to take a punt at an inexperienced manager, whilst we MAY unearth the next Jose Mourinho or SAF, it's more likely that we won't - and that means that players only have the club profile and the money to make their minds up on when considering whether to take a chance with us in their very short (albeit lucrative) careers.
Our club profile isn't great in the footballing world. We have spent most of living memory in the 3rd tier, so it's more likely that we would have to spend more on wages in order to compensate for that.
When an established player considers coming to us, he probably won't think of the chance of a glorious promotion with a big club. He will think of being a mediocre career at a mid-table championship club. Some will probably even still think of us as a 3rd tier club punching above our weight (lets hope this one doesn't come true).
You can see it in the mindset of other clubs' fans and even some pundits, when they post on their forums about playing against us - things like 'we should be beating teams like Bristol City...' etc. We call it arrogance, but it does give an interesting (if somewhat annoying) insight into the general perception of our club, as seen from outside. The Zack Clough incident, whilst insulting and infuriating, does also serve once again to remind us that within footballing circles we are still seen as an unfashionable club going nowhere.
Employing a well-established respected and proven manager would boost our ability to attract better players and that would in turn lead to greater success on the pitch. This would make a statement to the footballing world that SL really means business.
Won't happen though.