FireTom, just from my perspective as somebody who's new to poi, and who has always wanted to juggle (but still can't do more than the bare basics), I see as many similarities as differences, and I agree that if things like cigar boxen, hat manipulation, and things of that specialized nature are accepted by "traditionalists," then spinning should follow.
BTW, the light source observation belonged to MNS, not me; however, it is something I've thought about a lot recently... When I first saw poi in person (having only heard the word whispered in dark alleys), it was on fire, and by subsequent internet searches revealed a heavy focus on fire, so I developed the opinion that poi = fire dancing. Which, of course, it does, in one regard. It wasn't until I made a set of sock poi (my first practice poi were always as close as I could make them to fire props, since I assumed that's what I'd be using primarily) I started to shy away from the "Let's see you do that on fire" mentality that I think Internet Poi gives off to some extent. Of course by Internet Poi I just mean what beginners who are browsing the Net for poi resources are likely to come across.
Still, I've stopped thinking of it as a fire art, though it can be used in that way. There are moves that look great on fire or with LEDs or glowsticks or other light sources, but by the same token, some look better with socks. In your quote, Plumsie said some moves look like nothing if you can only see the lights. This is true.. TTN looks great if you focus on the body, but just the heads, it looks no different from a butterfly. Same with a lot of moves. A 5 beat weave doesn't really add anything to the performance that a 3 beat wouldn't if you can't see the body motions involved; it just looks like more circles. Yuta did a performance I saw on Youtube where you could *only* see the lights, and it was incredible, but to analyze, it was only "basic" moves, so you lose the richness of complex body motions, if you decide to use them in a performance.
I would go so far as to say that fire poi and sock poi are vastly different styles of performance, not because moves can only be done with one or the other, just that they look much better with one or the other. Flowers look like nothing with sock poi, but awesome on fire. Wraps and things look best when you see the performer, not just the heads.
I can understand Plumsie's sentiments that some performers use fire so they don't have to use skill, and even after only being involved with poi for half a year I'm starting to get a little bored with "fire poi," just because as she (he? *shrugs*) said, most are performances for which fire is only another feature, not actually part of the show. I actually feel the same way about most props - fire devil sticks, swords, rope darts, torch juggling, contact juggling (god bless Youtube), yoyos (haha just kidding)... The performances don't tend to be enhanced by adding fire. Hoops, staff, and poi are all things that I have notice people can make the fire do awesome things, the other toys it just seems like the fire is incidental.
Personally, I think if a juggling convention doesn't want a fire performances, I agree with this Plumsie character that it shouldn't be necessary. I love spinning fire, and I love being around fire spinners, and a great fire show can be awesome, but it's only one element of poi; it doesn't define poi. LED poi are great where fire is impossible or just instead of fire, but again, it doesn't define poi. For those patterns where the head is the primary focus, brightly colored heads with dark cords can do this without fire, but in a brightly-lit setting that still allows the performer's every move to be seen clearly.
*Shrugs* I'm rambling now, but 50 points for you if you read this far!

I'm gonna go read the IJDB thread now...