$100k/yr would be very nice, although I'd actually be satisfied with considerably less, especially since this has value to me beyond the money - I think it's a cool project which will be useful as a calling card no matter what happens. If I could reach $2000/month sometime this year I'd consider it a success!
My wife took a couple years off to work on her startup. It never really went quite where she wanted, but did "ok" (a few thousand regular users). When we decided we needed her back in the workforce, having it on her resume was a source of intense discussion during all of her interviews and was a big part of her landing the job she has now.
People talk about knowing the entire SDLC as important for jobs, but running your own thing means that the software life-cycle is a really small piece of what you do and those additional skills are very valuable in the workplace.
edit btw, last night I thought about asking you if you'd consider adding a donation button on the free tier. People may be intermittent users, think it's useful, but not want to commit to the paid tier, so they give you a donation instead?
It could be a way to transition somebody up to the paid tier later if they're regular donators. Maybe keep track, and if somebody donates a certain number of times, or a certain amount of money, offer them a discount for a year or something.
I doubt there would be enough donations of less than $4.99 to make it worth adding the option.