I'm not really sure what the Seton Hall argument is even about, but I'll chime in:
Coaching/recruiting is obviously more important that conference affiliation, but conference affiliation in this regard is only going to help Memphis. More exposure, more tv dollars and better competition. Those three things should be key in getting better coaches, retaining better coaches and getting better players.
Not sure what you want from Seton Hall though? They are probably better suited to be in the Atlantic 10 instead of playing with state funded institutions and the catholics that invest more into their programs. They've made some bad hires, like Bobby Gonzalez, but it looks like Willard could be a good one. The fact that they play in the Big East is probably the reason why they were able to get to hire either of those coaches.
The conference alone isn't going to obviously dictate your success but it's certainly a platform that other schools in C-USA or the A10 can't offer.
It's not just about Seton Hall.
The argument made by many posters in support of the basketball additions is "they are joining the big east, they'll be able to recruit better players, and therefore they'll be more succesful".
Yes, they'll be able to recruit better players. They are also going to play in a much tougher conference, and they are going face much better coaching. And there are a number of other teams joining the big east that will make that same recruiting pitch. there are also programs that have long standing reputations in the big east and will continue to sell that. bottom line, it will be coaching that decides the fate of these programs.