I just re-installed my phone and unable to download spotify from anywhere as 'marketplace' has ceased ,unfortunately as a premium member I cannot use it on my phone .Hence going to cancel my membership.
What's happen when you go with your mobile to m.spotify.com?
I think there is no option to download manually those apps, you are forced to update your phone...
On Windows Mobile 6 there is no resstriction to install Programms from Internet.
So if I Had the install file, i can install. Must be somethink like this "spotify.cab"
.cab is the File Type for installation files on Windoes Mobile 6