Personally, without an increase in airframe capacity, the new parts don't do much for me. They follow the same cost/upgrade pattern as the previous tiers, and using a single one will cost more than half your airframe capacity. IMO, the only airship design that should consider using one would be a re-design of an airship already using Tatanora class component(s).
(Components listed as: Hull/Rigging/Fore/Aft)
(Stats listed as: Surveillance/Retrieval/Speed/Range/Favor)
So: Frugal Freighter (Invincible/Bronco/Tatanora/Tatanora)(120/140/50/84/136) - Must downgrade a Tatanora to Odyssey in order to upgrade the other Tatanora to Viltgance.
Option 1: Invincible/Bronco/Odyssey/Viltgance - 102/154/46/84/122 - Even slower, more retrieval but less Surveillance and Favor. Maybe good if you want to gather a ton of stuff, but loooong trips.
Option 2: Invincible/Bronco/Viltgance/Odyssey - 138/126/54/84/150 - More Surveillance and Favor, less Retrieval, slightly faster. Maybe better chance for good items, but less items at a time?
Frugal Flier: Enterprise/Bronco/Odyssey/Tatanora (106/140/50/98/118) - Downgrading the hull just puts you in Option 1 of Frugal Freighter modification, so must downgrade the forecastle further.
Enterprise/Bronco/Invincible II/Viltgance - 88/154/46/98/104 - Surveillance below 90 makes this a no-go, imo.
Fortune Seeker: Invincible/Invincible/Tatanora/Odyssey - 124/122/68/80/136 - For the sake of argument, I will assume keeping the Odyssey Aftcastle is desirable. Therefore, one of the hull or rigging must be lowered. Dropping the rigging brings us back to Frugal Flier option 2 again, so we have:
Bronco/Invincible/Viltgance/Odyssey - 138/122/68/66/154 - Great stats for collecting, but with a 66 Range, very limited options for destinations (I think it can still hit everything, and a few 2-sector, but not many). Still might be a good upgrade option.
Eager Explorer: Enterprise/Tatanora/Enterprise/Enterprise - 90/78/132/78/90 - Need to keep the Forecastle or we no longer meet 90 surveilance.
Option 1: Invincible/Viltgance/Enterprise/Enterprise - 90/74/146/60/94 - Faster, slightly less retrieval, can't go as far. As long as it can still reach ever sector (not sure if it can), it fits with the purpose of the Eager Explorer pretty well.
Option 2: Enterprise/Viltgance/Enterprise/Invincible - 94/60/150/74/90 - Even faster, even less retrieval, less range penalty vs option 1. I think this is probably the best thematic upgrade of all the options in this post.
Since the only Tatanora-using airship I use is a Frugal Freighter, for me, Viltgance changes nothing.