Gidley's a crap option for bench. Every time he is on the bench there comes an awkward time about the 60th minute or so when the coach (and everyone else) realizes there is no real point in him being on the bench... But then they just put him on anyway, at some position like hooker where he inevitably just goes worse then whoever was there in the first place. Sure, it's good to have a "utility" that can play 10 positions on the field, but the reality is that's not really what is needed. In this Australian team especially having him on the bench would be a waste. Luke Lewis would be a much better option (see below)
Slater gets injured -- Hayne fullback, Lewis wing/centre (Inglis or Hodges can go on the wing if need be)
Hayne/Morris injured -- Lewis wing
Inglis/Hodges injured - Lewis straight swap
Lockyer injured - Lewis 5/8, Thurston could handle play-making duties
Smith/Thurston injured - probably worst thing that could happen, but that could happen every week with their clubs. Lewis could come and cover. Hell, a few years ago Crocker was Kangaroos 5/8 so I'm sure we could handle it with Lewis.
End of the day --> Gidley's rep career should be over.