Hello
I've played around with the Kobo Mini, Touch, and Glo before finally settling on the Glo. My reasons? It had built in dictionaries in many languages (Japanese is one and Jap-Eng is another so you know
); secondly, the built-in light was a huge factor. I bought the Touch, went home and tried to read later that night but OMG was it horrible.. So I returned it the next day for a Glo and never looked back. I had a play with Kindles and some Sony models too, but I didn't find the same satisfaction.
As for the frontlight in Mini (as you've suggested) I don't think they'd even do something like that? The battery life on my Glo is great (I switch off the WiFi unless I need to use it).
I think it comes down to personal preference. For me, I couldn't really buy the Mini because it had no SD card slot and for me, that's a big negative point. The size of the screen didn't bug me either, but it's the small things that count.
Someone with a Mini will most likely come past this thread and tell you what they like about their Mini and maybe you'd like what they have to say.
So if I were in your position, I'd wait. Simply because newer eReaders are being made and released and diving into an offer because it looks good now is not the smartest idea *blush* I speak from experience of buying a phone and then have the price drop $200 a week later..
But do have a play around with the Kobo range if you're interested. I would have put a Japanese book onto an SD card, plugged it into a Touch or Glo, and see how it reads and how the dictionary is for you.
Good luck!