As in all things tastes change, things move on, football is no exception, as you rightly say @Robbie the goalkeepers role has changed immensely and these days a goalkeeper has to have a range of qualities, they have to be good shot stoppers, accurate passers, accurate throwers and excellent with the ball at their feet to enable them to dribble when necessary. So in that respect I would imagine the clubs feel that a good goalkeeping coach is worth his weight in gold.
Who remembers George Smith the Notts goalie from the 50s early 60s, he would sometimes dribble his way out of goal and I’ve even seen him take a throw in halfway up the pitch, perhaps he was a trailblazer sweeper keeper.