I don't want to make too long of a post. My wife can email you more if you like. But you and your wife's points are very valid.
My wife has had 475cc smooth/round/saline/over implants for over 4 years now. She is about 5'5" tall, about 135 Lbs and was previously a 34B. She is now a good 34D/DD. But we had a conservative surgeon and she went in wanting 600cc minimum, but we didn't push the surgeon hard enough and when the surgeon mentioned only about 350, we only pushed for 400cc implants filled to 475cc. And about a year later when the implants settled, my wife was very dissapointed that we didn't stand firm on getting 600cc implants. So now we are waiting to see if we will have kids, and she will go larger later. So you do need to be direct and firm. But at the same time, that may also mean that you will need to be patient; as some surgeons may turn you down because of that. But if she is a C, and wants to be a good DD, then most likely you will want to be firm on at least 500cc. Just remember that when they have her use the "sizer" implants during consultation, that what ever they tell you, it won't look nearly as large as they do during consultation. I think they try to scare women into smaller sizes. Probably to have them come back in the future for a 2nd BA. Just be firm on what you want. She should basically come out of surgury thinking that her breasts look huge, because within a year afterwards, she will most likely feel they are either just right, or not large enough. Good luck on your consultation(s).