Tien,
I too was there at the weekend with the Yarra valley group.
I watched this thread with interest and I thought I might ad my persepcgtive which I think is a little differenct from the stock persepctive.
I have visited the old A to Z Bonsai now closed, Garden world and Bonsai art as well as the new iteration of the nursery at Mount Evelyn. Each is unique in there own way, and I hope my reflection is useful to you. I also indicate that I am a very enthusiastic beginner, so my perspective comes from lurking on the internet for a few years and almost two years with a club. So I guess my contribution to this discussion is about the visuals and the experience rather than the stocking itself, as other far more experienced have covered that quite well for you.
So let me begin by saying that all the nurseries I describe below have the same features such as providing all the right stuff, wire pots, starters and established plants, as far as I am concerned, and I hope that by outlining what I see as different might be of use to you.
I find that Bonsai Art is a very tranquil setting - given that it is very near main roads, and an airport, and that sense of tranquility puts you in a frame of mind to wander and contemplate. I can't really explain it any better, but would find myself spending hours there partially for the ambiance of the place.
Garden world is amongst a bigger more bustling series of nurseries and I am struck by the two types of bonsai on sale, starters and what I would call well established pre bonsai, ready for a final trim to become "bonsai" for the first time. (I can hear the more experience people on the forum going "what is he on about?"

). I find looking at stock while people in the cafe next to the window are sipping lattes to be slightly disturbing...

but interestingly I have never bought anything from there even thought I have been in about four times to "have a look". Can't really say why.
Mount Evelyn has been a nice place to visit an at the time I last visited it was still being established so the feel has most likely changed, but as my closest venue I would hope to spend some time there. But as it set up, it too had a more tranquil feel that I would associate with the nurseries in Japan -having never been there it is my assumption only.
Then I come to your nursery. Quite frankly I was blown away when I walked through the shed and into an expanse that I found quite daunting, and as such found it hard to take it all in. A few personal things that other locations have that I think would make the experience for me better, and therefore I hope for others, is to have prices on everything, as quite a few items didn't, and while most of the stock was in great condition, the odd dead plant here and there detracts from the overall experience. That said you had plants from $3 to $15,000 - I so wanted one of those
That said the location is wonderful, and of course I bought some tube stock, some more advanced training stock, and the really odd Chinese elm, that I have continually stared at wondering why I bought it, and then having fifty ideas flood in at once
So I come away from your nursery with a memory that I spent a great deal of time coming to terms with the flow and lay out of the place, and next time I visit that won't be an issue for me but for what it's worth, I find those nurseries set up with that flow and tranquility in mind speak to me as more authentic bonsai nurseries, again based purely on speculation on my part rather than any genuine experience.
So for me the visual and flow of a location is an important factor as well as the stock, materials, accessories and feature trees. I will definitely be back - especially if that pine tree is still there.
Hope this was of assistance.