Many fungus cards like Thallids grow stronger over time by accumulating spore counters, which you can convert into Saprolings
Chase cards, alternate art, and foil variants increase value potential
In fact, theres a popular deck in Modern and Legacy called 8-Cast, and the name comes from the deck running both four copies of Thought Monitor and four copies of Thoughtcast
That aside, lets look at Old Gnawbone
Well, that just depends on if theres a deck that needs it
When in Doubt, Always Get Lands Land cards are one of MTG 's defining features, and while they do contribute to MTG being one of the best TCGs of all time, unfortunately Wizards of the Coast tend to print powerful land cards, that become necessary inclusions in many decks, with the "rare" rarity