On the subject of staffs/spines, there were at least 3 other Rahkshi seen in the comics.
Two in comic 16 : an orange (or gold?) "Vohrahk" and a yellow (gold or tan?) "Turahk". It should be noted that in the books, this scene describes a Rahkshi of heat vision specifically.
In comic 22: a blue "Panrahk" (+ another in silhouette). Maybe molecular disruption?
I like the idea of a bin having randomized Rahkshi parts to mix-and-match. It's probably the most realistic way they could do it. And technically, there are only 18 unique colours, so it would be a little more manageable to collect than 42.
This makes me wonder what Bionicle would be like if they had more of a DIY approach like Hero Factory tried to. It wouldn't work the same way obviously, but maybe they release value packs each year with exclusive colours for other clone sets like the matoran. That way you could build some of the side characters, like Tamaru, or make your own more easily.
I'm getting off topic, but I can imagine having supplementary adaptive armour packs for the Phantoka/Mistika. With different fins, masks, or whatever else to customize the Toa.