in my opiinion practice essays are good only for two things;
1) to improve your writing style if that's where you're losing marks
2) to test you know your stuff and can handle a tought question
I think it'd bad to do too many practice essays or you become complacent but doing a few definitely helps
quotes are great and stuff but i'd focus more on techniques cause that's what you need to get in the top bands
especially if you're doing poetry, you'd want to focus on imagery, metaphors, symbols, aliteration etc rather than quotes
best of luck!