No theology, apologetic, dogma…. MUST be adopted to develop one’s self/spirit. In fact, Buddha often admonished his disciples not to blindly follow his teachings but test them and verify them through their own experience like a goldsmith tests the purity of gold.  I would go so far in saying that part of the journey will require one to move past and even reject all the dogmas and such. one must leave god to find G_d

The question you ask – do you have to fully accept this theory to develop myself – suggests that you may be miss-understanding the words ‘spiritual development’ so it might help if you state what you mean by those words.

As for the Law of Vibration – I suspect there is something to it – based on my own experience

I always liked the idea of string theory, where it is the vibration of the “string” determines how they interact and create matter.  I’m not sure if that applies to the Law of Vibration or not however I like the picture it creates…. Have you even done the experiment with a magnet and metal filings – how the magnetic field of energy a-lines the filings into the pattern of the field – all the filings vibrating in the same direction, each filing influencing the other to create the pattern… Or have you been at a concert were the music a-lines everyone and you have the experience of being connected to everyone, everyone “vibrating” in the same direction, experiencing the same ‘energy’, emotions….

“Every thought, emotion or mental state has its corresponding rate and mode of vibration. And by an effort of the will of the person, or of other persons, these mental states may be reproduced, just as a musical tone may be reproduced by causing an instrument to vibrate at a certain rate − just as color may be reproduced in the same may.” – Kybalion

You may be interested to read hermetic book Kybalion – you can download a copy for free, just google it.