This is a good topic Jason! And actually something I've been working on/thinking about a lot lately.
1. Speed. There's a couple of things I've seen people do.
First, how's the speed on the recall? I know some people do not feel like the recall impacts retrieve speed, but my experience has been different. If my dog understand Hier as front sit as fast as your butt can get you here...and I call Hier on the retrieve they should pick up speed. I have worked on return speed with toys as well before I ever incorporate the dumbbell. My dog's return just as fast in casual fetch as they do in the formal retrieve. I have seen long lines and prong collars used as well as electric to reinforce the "get your butt here fast" concept for possessive dogs who do not want to return with their toys.
Those folks who use a trade based retrieve usually have to increase the value of their motivator. I've seen people use helpers and sleeves to speed up the return when a ball or food isn't enough. Either that or compulsion starts to come into the picture.
The biggest thing that has helped me is getting my dogs to run back to play with me again. This is an OB video from training the other day with Cade. He's really starting to get the concept of returning to play. He's not as direct as I'd like him to be on the turn around, but you can see he picks up speed to come back and slam me.
2. There are functionally 2 different types of motivational retrieves. The prey based retrieve and the trade based retrieve. I sort of fall somewhere in between depending on the particular dog. But I think using the dumbbell as a reward in and of itself can be very useful in training the retrieve and in the routine. Consider the OB routine. The dog has to do it all on the hope of reward...What if in the middle of the routine the dog gets to play a game? A game with rules, but a game none the less. A dog that likes to retrieve for retrieving's sake and is rewarded by that gets a pick me up in the routine. The successfulness of doing this though is dependent on the HOLD and on your dog's general return behavior.
I don't personally like a totally trade based retrieve. This is a technique that is used a lot by AKC people in my area and it seems to be Flat in much the same way that a lot of obedience goes flat. It hinges on the handler's ability. I think it takes longer, takes better timing, etc because it is a complex behavior. I also think there is almost
always a "You HAVE to go out and get that dumbbell and bring it back" compulsion portion that has been more severe than the prey based retrieves I have seen. The most common problems I've seen with it have been lack of enthusiasm and commitment- arguably training problems because of the timing of the rewards etc. and the speed of the retrieve.
Argos was originally done with a prey based retrieve. I went a little overboard and focused too early on going out and coming back and not enough on the Hold. The enthusiasm and the speed were excellent, but the Hold was miserable. He got to the point where he couldn't think he was overloaded- My mistake. He would actually spit out his ball to go get the dumbbell. Most people who do the prey based retrieve have difficulty with the hold and the control. I had to go back and take drive out of the exercise until I could get it to a manageable level. I did this by reconditioning his Hold on a PVC pipe with a modified force method taken from retriever folks and then going back and using a trade based method for the retrieve. Now he's world's better but he seems to have retained some of his love for the dumbbell exercise more so than some other dogs I've seen who were only trade based.
We learned from the mistakes we made with Argos and improved with Anka. She learned the hold first as a marked behavior on her Ball. So she learned to Hold a prey object and she already knew how to bring it back because we worked with her on return of the toy like we are doing now with Cade. She learned to do the retrieve completely on her Ball before we ever introduced the dumbbell. Then it was merely a matter of transferring value to the dumbbell. It was actually funny because for a couple weeks all her obedience was done with the dumbbell as a reward. We vet wrapped it to protect her teeth and used it in the same way we had used her ball. This is a video of Anka doing the retrieves with her ball, at the end you can see how it was marked and rewarded with tugging. She's still polishing and has a couple of regrips on the return, but I love her speed and enthusiasm.
We've started Cade in much the same way as Anka. I'll probably begin training his retrieve in earnest this Winter. I'll let you know how it turns out.