ESC Warrenty?
I don't know if they give what would be noticeable speed or run time increases, but I would think the do a little.
The reason I feel this way is because the resistance in the Tamiya plugs is greater than that in the Dean's plugs. This means an increase in battery power going into the ESC/motor instead of heating the plugs.
I also think that part of the reason that Tamiya plugs melt is because the connection is loose between the plugs (not the plastic but the metal connectors inside). As the vehicle moves the connections move which causes arking between the plugs. This creates a loss of power through out the whole system. Remember a system is only as strong as it's weakest link.
With all of this in mind I would say that the Dean's plugs will give you more speed and run time. How much? Maybe like a 1/4 mph and 5-10 seconds of run time. Nothing perceptible for the most part but increases all the same.
The big difference is that you won't melt any more plugs or any future plugs and you won't be stranded after paying for track time because your plugs melted together (that's what happened to me). It will make a bigger and bigger difference the lower the turn motor you decided to run.
Besides it's not like the Dean's plugs are very expensive. I was able to do fit my charger, two cars and five batteries for $15.00. The plugs are also very easy to solder, but I recommend you use something to hold the plugs while you put them together.