It could be worth asking your current patrons/fan base about what they would like to see in higher tiers that would make them raise their pledges. Some fans might not have the funds, but others might make good suggestions. Just make sure that whatever you choose to offer, it’s something that you can do sustainably and at that price. Otherwise, it might just come down to growing your fan base and increasing your reach through marketing.
I’m not your target audience, I’m no programmer, but I’m a very visual person, and in looking at your page, the first thing I noticed was a lot of text with nothing to accompany it. It might help your page look a bit more flashy and attention grabbing to throw on some graphics.
I’d also consider either adding more goals, to help entice current/new supporters, or remove the goals entirely, since you only have one and you’ve already reached it. If you’re not sure of what goals to make, you could always ask your supporters for ideas too. What sort of things/projects would they be interested in seeing?
Seems like you’re doing well so far though. Best of luck