Ok there is truth to both sides of the argument here.
As I play both drums and bass I think I can make a somewhat fair assessment here.
Drum sets can get crazy big and eat up a ton of stage realistate as well as time to set up. I have been in been in bands with drummers that have 9-piece rocker kits that only play "boom tap boom-boom tap" drum lines that could easily afford to scale it down. Then again I have played with drummers that have larger than a 5 piece but actually sport a good sense of when to over play and when not to.
You have to remember that all the "extras" in a drum kit are extra notes, or effects. Telling a drummer to scale it down to a dinker 4-piece is like telling you to play the full set using only 3 frets on the A string, or telling the guitarist to not use his trust wah-pedals or distortion. You have to be careful with this topic and understand what you are asking.
I have seen just as many good drummers on small kits as large kits, just like I have seen a ton of crappy drummers on small kits and large kits. The worst for me is boring drummers. I don't mean flashy. I mean the same beat played the same way, using the same bits of the kit everytime. Having a larger kit can break the monotony if the drummer has any sense of taste. In your basic bar band a 4-piece is probably fine, but a bigger kit CAN help make things a little more interesting after 2 hours of listening to the same routine over and over. I agree with the previous poster that said more cymbals than drums.
My favorite kit that I've owned to date was a 7-piece which was a happy medium between huge and reasonable.
For the OP, one thing you may want to do with your band is to practice set up and tear down and time it. One of my early bands actually stop watched this, which was good because we carried a lot of stuff. Being in a wannabe Queensryche/Dream Theater/Kamelot style project we brought a ton of gear, including back ups for everything. Taking the time to work on bein efficient with our time was critical. How is stull loaded into the truck, which order does it come out? Who carries what? It helped deal with the "ton of junk" factor. If your drummer is going to bring the monster kit, it might be worth the time to work on this.
So in short - Don't automatically fear the large kit, just make arrangements prior to it becoming an issue.
