Yes, envelopes are trash atm.
Buff possibility? I'd consider it, but i personally refuse to back it without an understanding of the general workings of it. Leading with a comparison of mario and starman, not a good example. Starman A, makes you invincible and B, is placed in preset locations in specific areas, effectively controlling the destruction you can do since it will time out. (old mario) That also sums up my concern with buffing us, some areas could majorly buff the player before the benefit is honestly useful (last floor of peaca int anyone?) while others you wouldn't benefit much at all from a buff, and players would again feel the reward is useless. Give me +999 min/max in alby normal, just an example, i won't truly be killing faster as i can already kill everything there fast already.
Personally, i'd just put the envelopes only in reward chests, at the end of a SM or dungeon. At that point, i mean it's part of your reward. As such, i'd up the reward for doing said quest, significantly. Maybe revamp the requirements to clear all quests, while balancing the reward equally. Say if you had to kill 10 goblins for 5k gold, up that to 30 goblins for maybe 10k gold, similar effect to xp. That or trade off the xp/gold reward, for say a consumable item. Dungeons give pots, SMs can give unique crystals like Life Drain or Summon Golem. Anyway, general thought process that i have should have gotten across on that, so i'll stop there as i'm not trying to fully flesh it out.
Seeing the envelopes get changed into something useful, would be nice. I'm not sure how much time our staff's spent on adding and tweaking them, but i know someone did seem happy to get them working. So i really would like to see them become something that everyone enjoys.
When I say buffs, I mean buffs that are already within the game. One of the primary foundations of any suggestions I make is ALWAYS, always a simple implementation. I mean buffs as in receiving something along the lines of a weapon attack potion, a magic attack potion, HP/stamina/mana elixirs, a full recovery potion, experience boosts, monster drop boosts, or anything else you can think of along those lines. Just a disclaimer, once again because I know people reading this have insane knee jerk reactions,
do not be alarmed by the mere suggestions themselves. Hypothetically, a 0.01% chance of getting a 2x exp for 30 minutes should not be cause for alarm.
Being concerned with the timing or relevance to the player's playstyle I think is largely unimportant. Catering to the solo player's desire to ALWAYS get what they're looking for out of the envelope is a big mistake. I think what's important is the
possibility of getting something relevant. People love to gamble, and free gambles are the best gambles, especially if there's something you might like from it. Now, what this means for groups of players that have more diverse play styles amongst their party is that you might be able to distribute in a way that at least benefits somebody.
Solo Alchemist: you get a weapon attack potion. Who cares?
Party: You get a weapon attack potion. You pass it to the archer. They have a good time.
Even the buffs you desire might not always be relevant. Getting a weapon attack potion when you already one hit everything won't change the dungeon at all for you. However, in many cases, something like that
does assist you in that it might be the difference between one hitting a skeleton 60% of the time to 95% of the time, which is a
huge deal.
Again, the issue I see with the party quests is that unless the reward is significantly boosted (in exchange for reduced drop rates), there is no reason many people would go out of their way to do it. If I was running Fiodh Adv and it dropped a 10k goblin PQ (20k after boost), I probably wouldn't bother. To go all the way to ciar to kill 30 goblins for 20k is just not sufficiently rewarding. Pretty every quest would have to be seriously rewarding in an equitable manner for there to be any compelling reason to bother with them.
However, I do like your suggestion of adding them as end rewards in exchange for non-expiring buffs, but they would need to be seriously rare to avoid crowding out Shyla as an option. I'd totally go kill 60 goblins for an attack boost potion. LOL
Now, you actually bring up and interesting point. I don't know if the implementation of the envelopes is such that it's a GLOBAL drop, but if you could specifically tailor it to dungeons, you could create multiple instances of the item and tailor the envelope contents to the dungeon. I don't know about the dungeon chests, but I do know that the end-reward chests can be specifically manipulated. So that's a possible avenue as well.
Imagine running Math Adv and getting a 15 minute quest for killing 100 ceo golems for an enchant protection potion. Now that's exciting.