I agree it would be a really good and important thing to somehow provide enticement for existing owners to go in at a higher level. I don't need any more licenses for the full product, and that is probably going to be true of 90% of your supporters, so you are pushing the potential contributions down by making the "suggested" amount really low for your most loyal fans.
Also, you say if you can't get a few thousand to buy it it might not be worth doing, but remember that "there aren't 4000 willing buyers for the product" is nowhere near the same thing as "there aren't 4000 willing buyers who happened to come across a particular kickstarter campaign in a particular 30-day period." Plus, the general attractiveness of your software goes up across the board for everyone in the United States once this is complete, so lots of people are only likely to enter the potential customer or supporter base _after_ this project is completed.
I'm not sure what the incentives could be, though. How about, say, early access to the new feature as a beta tester? I'm sure others on here might have ideas, as well.
I kicked in an extra $10 for now, but will put in extra if you get close but are in danger of not quite succeeding.
(BTW, I love that somebody apparently donated to this project just so he could follow you wherever you pop up anywhere in the world and attempt to trash you for making scientifically supported recommendations about what software to use alongside MC. A little bit maniacal, but I guess he gave money to the project in order to be able to add those comments, so whatever.)