I also find hiragana-with-spaces hard to read, even as a gaijin. So I'm somewhat skeptical of the idea that Japanese and Chinese are harder to read because they don't use spaces. No offense to some people here, but I think it would be better to avoid coming at this from a position of "what is the secret that makes western culture so much better?"
After a quick search, there is at least some research out there that suggests that Chinese readers are able to read faster than English readers, e.g. https://www.tandfonline.com/doi/abs/10.1080/1938807990955829.... This comes at a cost though, and that is the time spent learning how to write, but maybe technology like word processors will reduce that cost while retaining the benefits.
>"what is the secret that makes western culture so much better?"
I wrote that example as an attempt to frame how Japanese scripts are written compared to English. If you thought it had anything to do with superiority and inferiority, you read between the lines too much.
Spaces can be used, especially in modern times and are sometimes used for even better readability, but generally and historically Japanese script is one connected string of characters with no breaks except for the occasional punctuation and line breaks.
A connected string of nothing but hiragana and katakana is very infuriating to read, with or without spaces, and as a practical concern the issue manifests quite frequently in any piece of longer-form writing that contains lots of foreign words (because foreign words are all written in katakana).
I'm not aware of such research but it doesn't surprise me at all. Chinese and Japanese have more bits per symbol and thus if symbols can be decoded in a similar timeframe they should read faster.
After a quick search, there is at least some research out there that suggests that Chinese readers are able to read faster than English readers, e.g. https://www.tandfonline.com/doi/abs/10.1080/1938807990955829.... This comes at a cost though, and that is the time spent learning how to write, but maybe technology like word processors will reduce that cost while retaining the benefits.