Form of Dracula, why is it written in letters and journals?

Annoyingly Dracula is written in letters and journals. I personally hate this form as it makes the book hard and stilted to read and stops you getting into the book. However Stoker may have chosen to write Dracula like this for versimilitude. By writing Dracula in this form  it helps to suspend the reader's disbelief and stops the questioning the whole book and say it hasn't really happened. I suppose you could argue that this makes the "horrors" (questionably) even more terrfying as it is putting on the appearence that it could all be real.

As well as this by using letters and journals it is an invasion of privacy. We as a reader intrude on the characters personal thought and feelings which other are not supposed to read, 'it is not intended for them' This personal invasion may help us to suspend our disbelief because as they are only writing to themselves or their close friends, they have no reason to exaggerate the horrors which have happened to them. If anything they would try to downplay it or reason with themselves and their friends with what they saw to try and prove that it was real and they havn't gone insane. 

Don't really know what to say apart from that so toodles :) xx