This quest is beneficial in the long run, but IT COMES WITH AN INITIAL LOSS!
When the quest is completed all trades in Loamm thet previously required Barter Bricks will now require Barter Boulders as currency instead.
Prices will be roughly cut in half in comparison, and you will acquire Barter Boulders in the same ways and amounts you prevously acquired Bricks (random drops from looting offerings, weekly quests...) meaning you will gather currency at the same speed as before, but with lower prices.
HOWEVER your old bricks will become pretty much useless unless exchanged for Boulders at a 3:1 ratio, which will be a considerable loss if you had many of them! If you are close to the number you need to make a purchase it might be better to wait before completing the quest and complete the purchase BEFORE you turn the quest in.
EXAMPLE: 1 voucher costs 80 Bricks (before completing quest) or 40 Boulders (after turning in the quest)
if you already have 75 Bricks you only need 5 more to purchase the voucher
if you complete the quest you will only be able to use the Bricks to buy 25 Boulders (3 Bricks to buy 1 Boulder): now you need 15 more Boulders to buy a voucher!
so it's better to get the 5 bricks you need, buy the voucher, then change to the Boulder currency
Unfortunately it's very likely that when you read this you'll have already crossed the bridge.
P.S.: any 1 or 2 Bricks you have as a leftover from changing them all into Boulders you can safely vendor, since you won't be able to acquire any more Bricks to make 3 and buy another Boulder. I suppose the very first Boulder you acquire by turning in the quest is meant to cover for this annoyance.