The expensive final ability does not trigger the second effect, but you'd rather have it as a mana sink than not have it at all
Most birds fly, so these cards are there to support the air squad
A 2/2 body for two mana is more than fair for an average goblin, but this would be better suited to decks with bigger creatures to support so the +1/+0 and Menace can
Rev, Tithe Extractor and Scythecat Cub are the two most expensive creatures in the set, and both have defied expectations by shooting up in value after launch
While there are build-arounds, it looks like you should be prioritizing the cards with the mechanic first, as they stand so well on their own
Some collectors will only purchase and sell in niche groups and will pay an added premium to stay off the bigger platforms