Taking a simpler mathematical approach, we can just determine the expected value of a new quest and decide based on that value.

For this calculation, it's important to take into account the quests' cooldown of 4 days. That is, once a quest has been completed, it can only reappear 4 days later at the earliest. Quests completed in the last 3 days as well as quests currently in the quest log are thus unavailable as the new quest (this includes the one we're rerolling).

As far as I know, all quests appear with the same probability, which is 1 divided by the number of quests available if the quest is neither currently in the quest log nor on cooldown, 0 otherwise. The expected value of the new quest is thus the sum of all the rewards of all available quests divided by their number. There is little research on this (most of which has statistically insignificant sample sizes), so this assumption might be wrong.

This is a list of all currently available daily quests:

- 40 gold: 9 two games with Win [class] or [class]; 9 play 30 [class] cards; 6 do some stuff = 24 quests
- 50 gold: 9 win 3 with [class]; 15 play x [keyword] cards = 24 quests
- 60 gold: 9 win 5 with [class] or [class]; 9 play 50 [class] cards; 1 Tavern Brawl = 19 quests
- 80 gold: 1 play a friend = 1 quest
- 100 gold: 1 win 7 games, 1 play 75 battlecry, 1 play 75 murlocs = 3 quests
- 1 pack (calculated as 100 gold): 1 spectate a friend = 1 quest
- Total: 72 quests

Now the Tavern Brawl quest only appears when Tavern Brawl is up, so from Wednesday to Monday (by rerolling at the right time, it's only truly unavailable on Tuesday), so when determining the available quests, take that into account.

So the best case, assuming one 50 gold quest in your quest log and 5 40 gold quests on cooldown, results in the following: 6 quests unavailable, 66 available. Total value: `19*40+23*50+19*60+1*80+4*100 = 3530`, which gives us an expected value of nearly 53.5 gold for rerolling the quest.

Worst case, you have the 5 best quests on cooldown (all 100s and the 80) on a Tuesday, leaving you with 7 unavailable (65 available) and an expected value of just over 49 gold.

As you can see, even in the worst case (all 4 100s, the 80 and one 60 unavailable), you only lose 1 gold on average. I'll calculate the break even point when I figure out how exactly to go about that.