I train both and I love both and they do compliment each. However gi->nogi is not the same as nogi->gi. ... Early on it doesn't matter too much like Easters said... At the higher level, you might miss a few grips depending upon your style of gi game, but I think the adjustment a pretty quick. When going from nogi->gi, there's a similar adjustment getting used to people gripping you (along with all the extra guards, chokes, etc) that there's more complexity but also the technical details are often missing. There's just less scrambles and slipping through or out of positions. You never had to pay attention to that level of detail to make the move successful enough.... I'm not trying to disparage a nogi rank. I just think that that's the way it is.
There is a lot of translation back and forth. So I'm also not in the camp that says even if you're a nogi brown, that you're a gi white... I think an instructor needs to do some evaluation and just bump up fairly quickly to where he thinks they belong.