I mentioned this on another thread, but the new MBP has reduced the number of connections I need to use when at home and "docked" with the AV adapter. The Dell has a few USB ports built-in, so it means when I'm working from home I just need to plug in the adapter and my speakers. With my previous MBA and Thunderbolt Display there were three connections from that and the speakers.
Did you try the Dell DA200 with the new rMBP?