A new stadium isn't even worth thinking about at the moment. As you've rightly said, building/re-developing is vital to Everton's future, and so it's imperative that Bill Kenwright and his mates have absolutely nothing to do with it. We'd just end up in a similar situation to Valencia.
Indeed the lack of vision is frightening. In the brief KEIOC period it became clear just how little the club knew about the Kirkby project. They just wanted someone else to do it for them.
However I think people overestimate how much difference a new stadium would make to our ability to compete.
Put it this way if we were given for free, and filled, a 70k stadium every week at current prices and sold 100 exec boxes at £50k a season we'd be £25m a year better off.
That would be enough to put us roughly level with Aston Villa in how much we could pay in wages. We'd still be £50m+ away from the current leading clubs.