Yes to both. It is an artifact permanent so it counts toward the cost reduction of affinity for artifacts. And since costs are determined and locked in before you get to activate mana abilities and pay, the reduced cost will stay reduced even if you sac the Treasure token for mana to pay for the spell.
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Former Rules Advisor
"Everything's better with pirates." - Lodge (The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science." (Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
Treasures you control are artifacts, so they count for the purposes of affinity for artifacts (C.R. 205.3g, 702.40a). After figuring the spell's total cost, if the Treasure has "T, Sacrifice this artifact: Add one mana of any color to your mana pool" and the total cost still "includes a mana payment", you can activate that ability (C.R. 601.2f-g, 605.1a), and this doesn't affect the total cost to cast the spell with affinity for artifacts (C.R. 601.2f).
Note that the Treasure artifact type (C.R. 205.3g) has no abilities or game mechanics inherent to that type, including the activated ability just mentioned.