You lose only 2 life when Cleopatra's last ability resolves regardless of how many counters the legendary creature that died had on it
In this case, Dungeons can be seen as just an extra bit of value on top of what you're already doing: a bit of life here, a scry there
Not even just the holos, but commons and uncommons like Eevee, Exeggutor, Butterfree, Rhydon, Weepinbell, etc
and because Limited play is almost always won on the back of creature combat, finding the opportunities to trade one creature, removal spell, or well-placed buff for more than one creature will pay off dividends
Once you have 5, it flips into Vault of Catlacan, a land that taps for any color or adds a blue mana for every artifact you control like the infamously banned land, Tolarian Academy