If you wanted luggage capacity sometimes, and speed others, you could always put something like a Yak Bob on the back of an otherwise nippier bike, and have the ability to switch. I've used my Bob on both the 700C Pompino and the 16" Brompton wheels, so wheel size shouldn't be an issue. When you're not using the Bob, there is only a slight weight penalty from the special quick release spindle, and you could swap that for a standard one when not using the Bob, if you really worried about the few extra grammes!
Admittedly, it would confuse and surprise car drivers, but most recumbents do that anyway!