Pfff, you could not be more wrong, you need to see it on big picture, season 1 and 2 was a set up for trials where Twilight learn, improve and pass tests alongside with her friends, season 3 started with entire empire being one big test for Twilight, and then there were just 13 episodes because it was made only for the sake of Twilight transformation ( though it would be better to sacrifice one episode so that finale would have 44 minutes time, 22 minutes was not enough for so much stuff ).



So long story short, season 1 and 2 were tests, season 3 was transformation with season 4 in mind, they probably worked on season 4 and came up with ideas what require Twilight as Alicorn and season 3 was just a set up for season 4.



As for what she can do in Ponyvile as Alicorn, A LOT, come on, Twilight being Alicorn close some doors to open new ones, it will make show less repetitive, now Twilight finished her study about friendship, but she need to get use to her new role, and her friends too.



RainbowDash can teach her how to fly, AJ can help Twilight improve strength and endurance of Earth Pony ( Twilight size increase suggest that she is stronger then normal Unicorn ), and as Alicorn she will have to improve her new magic powers and potential.



Furthermore she need to learn how to be good princess and ruler, she need to get use to being royalty and convince others that they do not need to BOW to her, that she is still old Twilight inside, maybe there will be diplomatic mission to other country for Twilight and her friends will come along, maybe we will get some info about Alicorns since Twilight is one, maybe we will get some backstory about Luna, Celestia, Cadance.



So yea, watch the big picture.