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.