You're underselling this hugely! $0.99 is far too cheap
It was this price point that got me to buy it to try it out. If it were $1.99+ I probably wouldn't have. Psychological stuff...
Is an in-app purchase required to offer something tangible? Instead of using ads and offering an in-app purchase to remove ads, I'd love to see cheap apps (ie: free or $0.99, without ads) with options for in-app purchases - maybe $3, $5, $10, $20 - that are nothing more than a voluntary donation to pay more for an app I find worthwhile.
If I could volunteer to pay more for apps after using them for an extended period of time (fully unlocked, no trial gimmicks), I'd likely have spent a lot more money than I have thus far. I won't pay thousands for a bunch of crappy used-once apps, but I'd pay a few hundred for the bundle of apps I've kept.