Usopp used them quite a bit. He also implemented some of them into Nami's Clima Tact.
or simply he will loss some comic relief with cola. Air dial seam quite potencial in fire based ambility to.Maybe save some dial for power up for future. But if Sh crew mainly luffy start use gadget zeff memento will be waste about spear of confident vs Don Crieg Wepons.
Well, ussop and nami at least were users of the dials in part 1. ussop used the dials for his previous slingshot and they were also an important part of nami's clima tac. Now, the question would be whether they still have the dials on their current weapons. Ussop seems to have a plant based slingshot but that does not actually rule out it having dials. Nami has an improved clima tac with the weather ball technology apparently but being trained in a sky island would not actually rule out her having dials. Dials are originally from sky island after all, perhaps it makes sense that the elders there would figure out a better use of the dials and weather balls than ussop would have been able to.
On the other side, i remember very well, that usopp upgraded Namis Staff with Dials. Its stated in the Rocketman when they prepare for Enies Lobby.
But yeah, since nami landed on Weatheria, with all theese strange weather equipment, she definately upgraded her Staff with Weatheria stuff. Like it was once hinted in the Cover Story.