Does group riding negate the aero benefit of deep rim wheels? I've been weighing up some options over wheels and in doing my research I've noticed that rim depth may be a bigger factor than I had previously considered. On the one hand, shallow rims are typically lighter and less susceptible to cross winds than deep rims - obviously the choice if doing lots of riding in hilly or windy areas. On the other hand, deep rims offer great stiffness (so more stability/handling improvements) and better aerodynamics, seemingly then the choice for flat low wind areas. 

But then I thought about group vs solo riding - when riding solo obviously the deep rims provide a maximal aero advantage. However, when riding in a group there is more slipstreaming going on, so aero performance should theoretically become less important (at least when not leading the bunch). This depends on how much slipstreaming advantage reaches the bike, I assume the biggest "hole in the air" comes at body level and that the bikes only punch a small hole which is unlikely to reach the bike behind unless very close.

My question is, does the aero performance of a wheel become dramatically less important when group riding?

I ask because I do a lot of solo training but want to maximize my speed for big group (~20-30 riders) riding events (vätternrundan and skandisloppet in Sweden), if the aero benefit is not reduced greatly then I think it makes sense to take deep rims.
The aero benefits of deep rims come from reducing the spoke length. Imagine that you're drafting behind a large truck at 25 MPH; you're not experiencing any headwind, but your spokes are still going around in a circle and slicing through the air. So reducing the total length of all the spokes (by using less spokes or shorter spokes) will give you better aerodynamics no matter what.

Look at what the pro road racers do (I mean besides the doping.) They use moderately deep rims on flat races, and only use shallow ones for climbing (when weight is a more important consideration).