Im not convinced allrounders are that useful as they are generally not used properly.
Too often they are expected to be both batsman and bowler and too often they are neither. Basically a 2nd rate bat and 2nd rate bowler that can weaken both the batting and bowling.
Unless an allrounder can make it into the team as a specialist in 1 discipline ie a Kallis or a Flintoff in 2005, then its often a bad thing to pick them.
I think its no suprise that the 2 greatest teams sine the late 70s (WIs and Aus) didnt have an allrounder and relied on specialists to get the job done.
Good allround cricketers can really help average - good teams, but the best tend to have quality specialists with quite clearly defined roles. Ill not bring the conversation onto Symonds and Watson
Obviously guys that can help out are preferable (like a Bevan or a Blewett or a Richards or a Hooper etc) but the bulk of the work is on the heads of the specialists. Secondary skills (like the batting of Marshall or Lee and Warne) are a joyful bonus.
As you said though, having a genius like Gilchrist at 7 doesnt hurt.