i think EE manipulation is fairly valuable, but i do think concerns about it are overblown at times. the larger category, the category 1 level up, of overall ee planning and management, now that is the level i would call 'huge'. but i do call a lot of things huge, and EE management is one of the things that you can do pretty little on and still be very successful. when you are trying to put together runs of championships and that sort of things, its one of the key areas where excellence is more or less required. but that's a pretty small crowd who aspires to those sorts of things, so certainly perspective is relevant.
the overall suite of EE management to me is really the combination of 1) understanding the mechanics of early entries; how likely are various players to leave and such, 2) directly incorporating such understanding into player evaluation (weighting not only the quality of players but how long they'll stay), 3) incorporating this into team planning as a whole (incorporating the understanding of which players will leave, and when, into team planning strategy), and 4) EE manipulation, or if you will, incorporating EE understanding into the player development strategy
i suspect most high end d1 coaches are at least doing *something* on those first 3, even if they eschew the EE manipulation part, and those are really the most important things. anything that feeds into player evaluation and team planning in a substantial way is going to be pretty darn important, and i think that is at least on this end, that is the most important thing. for a long time there was an 'EEs just happen, and man, it sucks!' attitude about EEs on the forum, and my main point is, you should be factoring that stuff in from the point you consider a recruit onward, and if you do, you can really manage the situation fairly well. i think this point is relevant to the OP here too!