Hey there! Welcome to the community! 🙂
Sorry for the trouble with Spotify and on car stereo. Spotify is aware of the problems with iOS and on car stereo - see here. Like one of the moderators said "We have been collecting a lot of feedback and we've been doing a lot of testing. This issue seems to be bigger than a simple "change this app setting and it'll get resolved for everyone."."
As for the iTunes subscription service rumor, it could take months, possibly even a year until is released. And then of course, they will have their own bugs after launching. By then, I'm sure Spotify will have a lot of bugs fixed. Now Spotify is currently testing some really cool features, which will be worth keeping Premium.
You said "...apple doesn't randomly delete my music while out forcing me to download it all again when I get home...". On Spotify, with offline music you have to reconnect to the internet every 30 days to keep them downloaded. Also there is a 3,333 offline track limit. It could also be a storage issues, such as not having enough storage on your phone.
By "switches off", what do you mean? Does the Spotify app crash on your device? Or it just stops playing music? If it just stops playing music, it could be someone else is using your account (usually you'll get a notfication.) Does this happen only when connected to your car?
If you want, we could look further into the issues you are having with Spotify here on the community - view this post for iOS. If your issues regard your car don't forget to add your car information (Car model, How Spotify is connected to your car, Versions of the media system, etc.)
If your case is resolved, please click the 'Accept as Solution' button and add your kudos!