How does the handwriting in the ciphers compare to the handwriting in the letters, is there any comparison and analysis on this? The first cipher looks neater than the Z340 (to my eyes any way.) Obviously there are a load of symbols in there which can’t really be compared, but still, thought I’d ask.

If you are talking about comparing ciphers to handwriting: Apples and oranges.
If you are talking ciphers to ciphers, that can be done which is how hoax ciphers are ruled out to all but a few amateur sleuths

One thing that is discernable between the letters and ciphers is the Zodiacs mental impatience. No one knows for sure how busy he was (he surely had time to devise ciphers and kill people), yet he speeds his penmanship near the end of his letters, and speeds his drawings at the ends of his ciphers, as if he had somewhere to be. His writing becomes messier and he breaks from his patterns in the third part of the Z408. The characters at the end of the Z340 also become sloppier.

It makes me wonder if the Zodiac had the patience to make the "Peek through the Pines" card; probably not, but some one sure wanted everyone to think so.

And did he really have the patience to surreptitiously plant all those "references" that a lot of people like to discover in the Halloween card? Again, probably not.

But, that’s only me thinking out loud.