Hope you're not insinuating that POLAROID cameras are not for instantaneous fun and joy. If you are i'll like to point you towards the 'Meet The Swinger' commercial for a 1965 Polaroid camera costing only US$19.95. Cute and portable too. Far more so in the 60s.
Video Link: http://youtu.be/h7k2uwJmwxo
Polaroid wasn't always expensive; they cost the same or even cheaper than Instax before their films were discontinued in 2008. Afterwards prices for original Polaroid film skyrocketed to up to $50-60 for a pack of 10 pictures for Polaroid 600; you don't want to know how much a pack Polaroid Time Zero film, meant for Polaroid SX-70 seen above went up to and still commands today.
They were also never 'extremely niche' - may I ask really, where and how did you get that idea? The rainbow OneStep SX-70 camera from 1977, according to Wikipedia 'the $40 Model 1000 OneStep using SX-70 film became the best-selling camera of the 1977 Christmas shopping season'. After that came the many OneStep models for consumers and the 'prosumer' successors to SX-70 like the SX-70 Sonar, SLR680, SLR690, etc which were VERY popular. Just not too much in Singapore but they still had a presence - check out Clubsnap threads from the past.