Despite the strategy, you'll be far from passive when playing with this deck, and it can be a lot of fun to endlessly frustrate your opponents who are desperate to send their biggest creatures your way for devastating attacks
For years, they were the engines of Standard
This also works as a win condition by first producing infinite mana, and then casting Venser with his two ETB triggers being an opponents permanent of choice + Venser
The other thing about Spirits being a typal theme is that as more cards are printed that let you choose a creature type to get benefits, there will always be cards to pick up to improve your Spirit deck
Card prices are driven by supply and demand, but also by history, rarity, collectability, tournament relevance, and formats like Vintage, Old School, and Premodern
Of note, Fortunes Favor targets and Saurons Ransom chooses, so you can choose an opponent with hexproof with the newer version