I guess determining what you rate as a seperate peak is really the question. This no doubt varies considerably upon your own personal point of view.
Your no.1 on the list for example, Ruapehu, actually has 12 "official" peaks alone on it (Tahurangi, Te Ataahua, Paretetaitonga, Te Heuheu, Tukino, Dome, L Peak, Pyramid, Cathedral Rocks, Glacier Knob, Mitre, Girdlestone) - and even some of these are open to interpretation as to whether they're classed as seperate peaks or not. In fact it's one of the classic alpine challenges to climb all 12 in a day by the way. I tried it once and only managed 11, so that is still on my very long to-do list!
Of course for the purpose of peak bagging, I think it's obvious that we can look on Ruapehu as a whole, and treat it as one seperate mountain with just one peak to knock off to claim it as a bag -ahh, but which one...

So if we treat Ruapehu as one peak, then, Ngauruhoe, Tongariro and Taranaki seem obvious picks after that. Fanthams Peak did surprise me a little for being on the list, as yes, I'd consider it more just a bump on the way up Naki as well. Sure it's named, but so are all the other peaks on Ruapehu. It's a bit like Girdlestone or even the Great Pinnacle (yet another one!) on Ruapehu in that respect - both peaks on the side of it which are also named, and more prominant.
You may have opened up a can of worms here Vino, but an interesting subject to discuss never-the-less. It would be interesting to see if there is a "top 10" list out there somewhere for fellow nutters to obsess over.
By the way, if you fancy another taste of the white stuff, I can see a winter climb up the south side of 'Naki, taking in Fanthams on the way for you next year if you're keen. Sure beats the scoria!