Harris offers zero impact other than goal kicking. Let's not get ahead of ourselves. He is solid, yes, but coming on with 20 to go he isn't going to impact general play in any meaningful way. Wasted bench option.
I agree with you on this for the most part. He isn't going to change the game through X factor or general brilliance, but as you mentioned, his goal kicking is first rate, it has and will win games.
In regards to his selection on the bench for the Wallabies, it can be viewed as a waste, but only if you take Deans' use of the bench out of the equation. It doesn't matter who the backs are on the bench, Deans' very rarely uses them in a manner which, allows them to have any game changing impact anyway. The only example I can think of contrary to this, is when Deans subbed Cooper on against Italy in 2009 and he stole the win.
Harris' selection ties in with Phipps, A.Fainga'a and every other bench back Deans has picked. The backs are only there for cover in case of injury or severe shitness. As cover and for Deans' use of the bench, Harris is the perfect choice.
I hope I don't choke on these words, but I actually agree with Deans' use of the reserve backs. I think the backs should play the full 80 minutes and should only be replaced due to injury, shitness/lack of effectiveness i.e Beale in Game 1, Barnes Game 2.
The starting backs should be our best players available, shouldn't get tired, so should play for 80 minutes. My biggest criticism of Deans' use of the reserve backs, are some of his selections and how long he takes to make the subs when it is clear a player is either ineffective or having a shocker or in some cases injured.
Forwards on the other hand should be subbed to maintain work rate and rate of effort, not just for injury, shitness or ineffectivenss.
Harris should be given 20 minutes from the bench to see if the combination of Cooper, Harris and AAC (Adam Ashley-Cooper) has potential. I think there is a possibility that that combination could work quite well, as he is a solid 12 who can pass and take on the line and create space on his outside.