Handanovic is top quality. Icardi, Kovacic and Shaqiri are all very promising players and should become top players. Guarin and Hernanes arent as good but should do better as they have done better before. Inter has good players its just that they can't find a system that works and have a terrible mentality. Milan are in a much worse situation because they dont even have good players.
I think Inter are only a matter of time. Mancini was always very good at bringing in cheap players that turn out great (Maicon, Stankovic, Julios Cesar, Figo, Samuel, Cambiasso, Maxwell, Crespo, Chivu) and he did a similarly great job at City bringing in Aguero, Silva, and Yaya which are their main players but ofcoarse none were cheap.
I trust his eye for talent and I think its only a matter of time before Inter become a decent team. I doubt he can make them a top team though.