We don't have a video this time around, but someone going by the name of Timelord Pony used his Tardis to teleport 5 years into the future and take screenshots of the completed game, all 6 elements of harmony in tow. Seriously though, the final unlocks are straight up insane. 600 gems for the town hall, 340 for the clock tower, and of course Rainbow Dash and Rarity coming in at 500 and 90 respectively.
I'll let him explain it though. Head on down past the break for the synopsis and images to avoid spoilers for those that want to grind it out for the next year or drop a gaming pc worth of money into it!
Timelord Pony's grindy windy synopsis:
Besides Rarity (90) and Rainbow Dash (500) you're also required to purchase several of the buildings and decor that require gems before finishing the game - this includes Town Hall (600) and Large Clock Tower (340) and several others that cost a bit less. Many are "skippable" for less than the cost of the actual item - but you definitely can't skip Large Clock Tower.
Scootaloo (50 hearts) was the only social element in the game that was not skippable via gems. Zecora (30 hearts) and the higher tier heart-unlocked ponies were not required.
After defeating Nightmare Moon (which is unfortunately a nearly-exact duplicate of the pilot rather than having an alternate conversation with Celestia asking "How could you fall again, Luna?" or something) you get a few "epilogue" quests that ask you to get Shining Armor and Cadence.
After getting both of them and completing a simple quest for Shining Armor to prepare him for a date with Cadence there are no more quests.
It's also worth noting that once you defeat Nightmare Moon you get Princess Luna in your inventory that can be placed into your town.
Princess Celestia, Luna, and Cadence all come with a full 5 stars by default - you cannot run minigames with them.
Someone also sent a video!