"I had planned" is in the past perfect tense - but 'Ich hatte vor' is past simple of 'ich habe vor'. In past perfect it would probably be something like: 'Ich hatte vor gehabt.'(Not sure about that though, sounds weird!) Shouldn't we stick to the simple past here and translate: "I planned to become" instead of "I had planned to become"?
I agree here, except in past perfect it would be "Ich habe vorgehabt" not "ich hatte vorgehabt". But yeah, I think "I planned" is a more appropriate translation for something in praeteritum.
When there are verbs like "haben" "sein" modal verbs and some other very common verbs, you tend to use always the form with präteritum.
Maybe the same goes with verbs that derive from haben.