Once you are spoiled it is over. The person has either spoiled you or is in the act of it. I suggest that the person is in the act of continuing to spoil you. As usual, you are trying to spoil me. As usual, you continue to spoil me. You shouldn't have, like always, you are spoiling me.

Thank you, you are always spoiling me. Personally I like to say the thank you first although some people may think the thank you should come afterwards. Any way you say it just saying something shows you appreciate the gift. I also like Joes answer 'I always love it when you spoil me' but I would still add a thank you.

It works, yes. But I hear "you're spoiling me" more often. Or "I always love it when you spoil me."