I have never worn aqua socks, but I expect that Fivefingers would resemble them somewhat functionally since Fivefingers were originally intended to provide good traction on a boat deck. I have not looked at aqua socks in a long time, but I believe that the sole of the Fivefingers will prove more durable and will be thicker on the toes, heel, and ball of the foot than the soles of the aqua socks. The separated toes are nice, but it is also possible that rocks or sticks can get stuck between the toes — requiring a stop to remove them. (I sometimes have to do this with traditional trainers that have a hollow spot in the heel where rocks can lodge.) With either Fivefingers or the aqua socks, if you step down a largish stone, you will probably end up with a bruise. The last time that I ran in the Fivefingers, I underestimated the amount of loose gravel on the roads near my house and bruised my feet such that I had to stop and walk home to avoid further damage. When that happened, the bruises did not seem to be very deep and did not affect my running in my more traditional trainers. My feet must be tougher from running regularly on gravel because several years ago I did get some deep bruises through my traditional training shoes that lasted for a couple of weeks and affected my running until they healed.
Perhaps it is possible that I could grow acclimated to running on gravel in Fivefingers. Right now, however, running fast is a higher priority than running in Fivefingers. The Fivefingers are not going anywhere.