The downside is your opponent can pay one mana to negate its effects, but if you can play Mana Tithe when their lands are exhausted and they aren't expecting a counter, it can still be effective
Not the cheapest of cards but I dont see that changing without a major reprint for the card which is impossible as it is part of the reserve list
Recently, we got some pretty powerful spirit dragons commanders in Tarkir: Dragonstorm
Goblin Chirurgeon, Coat of Arms, Skullclamp, and Impact Tremors are some cards that are commonly seen in Krenko, Mob Boss Commander decks
Key Creatures & Spells: Plaguecrafter, Fleshbag Marauder, and Merciless Executioner keep opponents boards in check every turn
Potentially, that's four +1/+1 counters per go around the table