Is it worth using the most expensive salvage kits on low level items

Pure tanking:

You are correct that the bears are the most adept at tanking in this game. Their stats at level 80 is:

• Power 1,374
• Precision 1,374
• Toughness 1,374
• Vitality 4,122

This gives them the highest health of any species of pets out there. In addition the bear is the best tank as they have a skill called Defy Pain which allows them to take no damage for several seconds. They also have a skill called Bite which allows them to regenerate. The bear that is also especially adept at tanking is the Black Bear. It has a skill called Enfeebling Roar that allows them to weaken all nearby foes, reducing their damage by 50%.

Pure Damage:

Your belief that a devourer would be advantageous in support damage isn't quite right. Their stats at level 80 do not have any advantage in power or precision. Their skills aren't particularly superior in the damage department. In fact it focuses more on defensively maneuvers. The main advantage they have is being ranged. In this case, either you would have to the "tank" which is never a good idea for a ranger or the devourer's range is useless since the enemy would just come straight up to them.

The Lynx has precision that is higher than most pets. They also inflict vulnerability which increase the damage the enemy takes and bite which is a burst damage skill. They also inflict two sources of bleeding which stacks intensity and duration. Another species of pet that is adept at pure damage is the Canine family which includes the Alpine Wold, Fern Hound, Krytan Drakehound, and Wolf because they have superior power stats. At level 80, their stats are:

• Power 1,718
• Precision 1,374
• Toughness 2,061
• Vitality 1,718

1,718 Power is the highest power stat for landbound animals.

Buffs/Support:

The Fern Hound has a skill called Regenerate which regenerates itself and all nearby allies. In addition, its species skills allows it to cripple and knockdown foes.

The Raven and White Raven are able to grant swiftness to all nearby enemies. In addition they are able to inflict blindness on the enemy.

The Moa specie is especially adept at support buffs. Their specie skills include a heal that also heals nearby allies. The Red Moa is able to grant fury to all nearby allies which increase their critical chance by 20%. The Blue Moa is able to use Protecting Screech which grants protection to nearby allies which reduces the damage they take by 33%.

Underwater Tank:

If you want a pure tank underwater pet, the Armor Fish is a terrific choice. It has the highest armor rating of all the pets and has above normal vitality. At level 80, their stat is:

• Power 1,030
• Precision 1,374
• Toughness 2,404
• Vitality 2,061

To supplement their tanky stats, they also have a skill to add protection to themselves which decrease the damage they take by 33% and have a heal.

And of course as mentioned earlier, the Bears are great at tanking due to their superior health. The bears are Amphibious which allows them in water and on land.

Underwater Damage:

If you intend to have a huge underwater damage dealer, there is no better choice than the Shark. The sharks at level 80 have the following stats:

• Power 2,404
• Precision 1,374
• Toughness 1,374
• Vitality 1,718

They have the highest power compared to any other pets on land or underwater. They have 3 sources of bleeding which stacks damage and Feeding Frenzy increases their attack speed.

So far only trinkets have ascended versions. A list of all ascended items and how to acquire them can be found on the official wiki.

Vials, Globs, and Shards of Mists Essence are used in the creation and promotion of ascended back pieces.

Infusions are upgrade components that can be added to ascended equipment. Infusions come in four basic types: offensive, defensive, utility, and omni. Offensive, defensive, and utility infusions can each only be used on their respective type of infusion slot, while omni infusions can be used on either offensive or defensive slots. Infusions crafted in the Mystic Forge will have agony resistance +5, those obtained from laurel merchants in WvW will have +1% damage to guards (for offensive) or -1% damage from guards (for defensive), and those from PvE laurel merchants have neither.