Is +1 Quest slot research for 120 stars worth it?

[Tina]

The title, basically. Being able to complete 6 quests per game (5 + 1 replacement) is good for prestige grind. But now looking at all the cool stuff I'm missing (like loot frequency, loot rarity, coins generation, and even little damage / attack speed / range boosts) in exchange for that extra slot makes me doubt if it's actually worth it in the long term.