A good comparison between the differences is:
- Ele sempre quis estudar Inglês = He has always wanted to study English (a desire that he kept during his life, and isn't fulfilled yet or wasn't until now).
- Ele sempre queria estudar Inglês = He was always wanting to study English (every oportunity he had, he wanted to study English)
The word sempre gives a little twist in the general idea of the tenses. But if you look closely, it does the same in English.