Might be my mistake AJ. I thought the thread title was “hidden features”, not “new features only”.
No worries, it’s a good one… see below (from the OP):
Not a new feature, but at first look possibly underestimated.
The manual is designed differently, and better.
The Help Menu now direct users to the internet for a version of the manual (rather than going to a PDF downloaded on the machine.
Here you can see the full manual, or you can download a PDF. The source for these PDFs is here:
This page is sometimes available and sometimes hard to peck down.
This way, if you want a fresh PDF (including the standards like Groove Agent, MIDI devices, Retrologue, and friends, they are there for you.
Z
It can be very useful if you want to work on a short section of MIDI (for example editing a 1 bar hi-hat part) whilst hearing it in context of your whole song. i.e. the 1 bar hi-hat part cycles round every bar whilst all the other tracks in your song play from start to finish.
Thank you 
New section in Preferences:
File / Preferences / Editors
For editor preferences and lower zone behaviour.
Jamming. Work out a 4/8/16 bar loop, hit play, and noodle away over it, then when you’ve found something you like, lay out the actual midi parts and record in. Saves you messing around with the project structure when you stumble across something 
(EDIT) - or can’t you record the midi into the project while just having the loop underneath it or something? Something like that anyway, great if you want to play with filter cut-offs and stuff and record those happy accidents. Been years since I’ve used it to be fair.
Note input for EQ frequency on stock EQ.
Oh, that’s very nice! is that new in C9?
Sampler track has many extra controls hidden as controllers
Frequency plug-in ‘Auto Listen for Filters’ button, allowing you to listen to one filter in isolation when you click on any one of its parameters.
Prefs/Chords and Pitches
Now has an enhanced set of features - includes “Custom Chords”
Also one more chord font
Beside new tags, when you setting custom tags in mediabay in Musical/Key now you can set octave for every key. Nice.
Best feature, a checkbox in prefs to actually enable Edge Hints! 
This is simply worth NOT Missing.
Have a click and drag of the three little dots in the new lower zone transport bar (there are several of these). You just might find that ‘go back to the beginning of project’ button, you were wondering about, or some other useful bit
Z
Loving the new Instrument Panel option allowing you to show only 1 enlarged slot that is sync’d to your arrange window. Makes finding the correct instrument so much easier than before:
Regarding sample track: That’s not “basic” and fully automatable / assignable with track controls, nice!
It is a good thing. But… and sorry to sound snarky Dave Nicholson… but NO SCROLLBARS dilutes this value for me a great deal.
Don’t you see the scrolbar in the right instrument window?
Slightly off topic… a new feature to me in 8, was memzap? What is it? it’s teleporting