I would say if you were going to elevate anything after the 9000 it should be the Symbian devices- i had a 6600 and a friend had a 6630 and those will to me always be the first "Smartphones" We played downloaded multiplayer games over Bluetooth in school, and though mine didn't have official mp3 functionality I downloaded the app used on later devices and used mine as an mp3 player. Even downloaded a bunch of roms for the ngage that ran just fine.

In the end though the peak for me was Windows mobile, everything up to 6.5 was literally just a pc in your pocket, after that they made the mistake (imo) of trying to compete with apple and android for user experience and failed miserably. For my part I never wanted the improved UX- a start menu style system with a stylus was great for me. Nokias N900 was great, but in the end too niche to compete with HTC and Apple when they were pumping out androids and iPhones. I handled purchases at my work for smartphones and gave the HTC hero as suggestion for my colleagues since it was simpler and got a N900 for myself, and though I liked it a lot android certainly went a lot further in the end.