Guild Wars 2

I’m just confused as to whether or not the rewards of the stuffing and cogs are just a once per each instance event. Or whether it’s something that resets with dailies?

The reward resets for each city. You get the stuffing and cogs reward the first time you run the instance in the city Tixx is currently hovering over. He sits over each city for 24 hours until he gets to Lion’s Arch.

^ The above answer is correct.

Just to add to the thread, the rewards are:
250 stuffing or glue (your choice)
100 cogs
1 toy plan (depends on the city)

So at the end of the 5 days, you will have enough mats for 2 toys.

I’m not sure if the rewards will persist after the 5 city visit.

Once Tixx has visited all of the cities and reaches Lion’s Arch, you can play through the dungeon of any of the cities that you missed, and receive the rewards the first time through.

My impression is that you only get the rewards the first time you play through each dungeon. I expect that to still be true once Tixx is in LA. (You won’t get the rewards a second time if you re-play one you’ve already finished.)