What is kept and what is reset for New Game+?

bastion

I've reached the point of no return in Bastion's story. I know that there is a New Game+ option, however, my decision on whether or not to go forward with the story at this point hinges on what is kept and what is reset. For example, I don't want to drive myself crazy trying to finish all the Proving Grounds if they're just going to be reset in New Game+.

I'm currently running on the assumption that your level is kept, but otherwise, I'm unsure as to what all resets. I'm wondering about:

Vigils?
Proving Grounds?
Weapons and their upgrades?
Buildings and their upgrades?
Accessibility of Secret and Weapon Skills?
Who Knows Where progress?
Items in my Pack?
Number of Fragments?

Please feel free to mention anything I may have forgotten that is not included in this list.

Solution 1:

Things Kept

Level & distillery spirits
Fragments
Weapons, their upgrade level, & items used to upgrade weapons (the "Something X" items)
Secret Skills
Most vigils (see below)
Leaderboard scores
Idols

Things Lost

Momentos & associated vigil
Buildings in the Bastion & associated vigil
Access to Who Knows Where
Completion of Proving Grounds & associated vigil

Additional Information

Weapon Swapping

While you'll have all your weapons for the new game, you won't have the ability to swap right away. Because of this, if you pick up a weapon during the story, you'll be stuck with it until you find an Arsenal. This adds a little motivation to upgrade weapons you don't use often that are also part of the first part of the game, where Arsenals are scarce and don't appear in each level shortly after you find the new weapon (like they do in later levels).

Proving Grounds

You mentioned that you don't want to finish the proving grounds if they will reset. While they will reset, you still get to keep the skills, items, and fragments collected by completing them before the game resets. Depending on how worried you are about updating or getting skills, it may be worth it to you to complete at least the vigils for your go-to weapons anyway.

Bonus Fragments on Level Completion

Since I built the Shrine in my New Game Plus, I've been playing with all but two of the idols active. I've also been receiving 2500 bonus fragments when I finish a level. I think it's tied to the idols and not some combination of idols and New Game Plus, but I can't confirm since I never played with more than one idol active in my original play-through.

Solution 2:

Here's everything I can recall:

Your level is kept, in addition to any potions you had bought/unlocked. This includes ones that you got through upgrading the Distillery.
Your progress on all the vigils, except for the vigils involving collecting enough momentos(this one is reset), making buildings in the Bastion, and completing all the Proving Grounds(thanks Shaun), is retained across playthroughs.
Weapons and all of their upgrades are retained across playthroughs. As soon as you get access to the arsenal, you can use whichever combination of weapons you want. Upgrades on the weapons include the Tier 4 and Tier 5 upgrades that you would normally have to access the Forge to make; in New Game+ the Forge acts as if it had been upgraded already as soon as you make it.
The upgrades on all the buildings, except for the Lost-And-Found, are retained between playthroughs. In addition, you can make the buildings in whatever order you want in a New Game+.
All your secret/weapon skills are kept.
It's difficult to say what actual impact completing Who Knows Where has on any other aspects of the game; that being said, the vigil involving completing one Who Knows Where section with an idol activated is retained between playthroughs, so I would assume that yes, completion of Who Knows Where is retained.
The items in your pack are not kept between playthroughs, but any upgrade items you had for the Forge will still be there when you enter. I believe, but have not confirmed, that the Gel Canister special item is added to your pack in a New Game+.
All the deities you've unlocked are still present in the Shrine. You have access to all the deities in a New Game+, for maximum difficulty.