As I think you have realised some of your issues (ads and artist payments) could be solved by paying for premium. Premium customers also get access to some music that isn't available for free (and early access to lots of new albums).
I think the problem for you though is the music you listen to. I have never seen music start to disappear (and I listen to a wide variety of music). It's also not reasonable to expect artists such as the Beatles to be on Spotify. They've only arrived on iTunes after years of Apple trying to get them. There is no way they will ever let you stream their music for free on Spotify.
EDIT: And as jsherry said the Stones are on Spotify. I have a lot of their stuff in playlists and listen to them regularly.
I think the best way to use Spotify is in addition to iTunes. I use Spotify premium to listen to music that I would never buy. And then I buy music from iTunes that I regularly listen to or isn't available on Spotify (like the Beatles). For the price of one album a month I don't think that is a bad way to use the service and probably how the record labels hope it would be used.
I never noticed the loss of the Beatles, Queen, Pink Floyd because I already had the albums and they were pulled into Spotify via Local Files.
In the UK albums and tracks on Spotify often have a "Buy" button (links to 7digital) so you can guarantee access and high quality. But I think they are missing a trick by not showing music that is not streamable but can be bought. This doesn't help the Pink Floyds of this world but this would work for plenty of indie acts.
> I think the best way to use Spotify is in addition to iTunes.
I agree. I previously used Grooveshark for this purpose, but the number of times I found mislabeled or corrupted tracks sparked me to switch to Spotify a while back.
A win for iTunes over Spotify, for me, is AirPlay. I know I could use AirFoil with Spotify and achieve much the same thing, but then I lose the (fabulous) remote control from iPad/iPhone capabilities.
My bad about The Stones. To be clear this is my parents' taste in music rather than my own but lack of their favourite artists was enough for them to dismiss Spotify out-of-hand.
I think the problem for you though is the music you listen to. I have never seen music start to disappear (and I listen to a wide variety of music). It's also not reasonable to expect artists such as the Beatles to be on Spotify. They've only arrived on iTunes after years of Apple trying to get them. There is no way they will ever let you stream their music for free on Spotify.
EDIT: And as jsherry said the Stones are on Spotify. I have a lot of their stuff in playlists and listen to them regularly.
I think the best way to use Spotify is in addition to iTunes. I use Spotify premium to listen to music that I would never buy. And then I buy music from iTunes that I regularly listen to or isn't available on Spotify (like the Beatles). For the price of one album a month I don't think that is a bad way to use the service and probably how the record labels hope it would be used.