Regarding cover art retrieval in iTunes.

* Can I do this without entering credit card details to create an account?

* Will this delete any existing (unwanted) artwork?

you can buy an itunes music card from a shop to establish an itunes account without the need for credit card details, just buy a $20 card...

it will not delete any existing art associated with the AAC file or ID3 tag of MP3s, but you can tell it to look for better art to replace the existing art...

then take a look at coverscout from equinux to get your whole library shining...

if you have a whole bunch of old mp3s it is also sometimes a good idea to update all their ID3 tags to version 2.4...

edit - then you can get into the whole super organisation of metadata like genre and disc and track numbers...

yes

no