Try it. What have you got to lose?
A good rule of thumb is that if you want your company to have revenue, you should require regular payment (make money while you gain traction, then sell or continue). If you want to have as many users as possible, you should make your application free (gain traction, investment, then sell or start charging). And if you want to optimize towards the fewest users, least revenue, and exude the least confidence to users, investors, and the media, and guarantee you'll be an employee of your existing company for another couple of years, have a donation system.
Soon you will find that as many people pay $2-$5 as those who would be willing to pay $30, if $30 was a standard price. If your goal is to minimize the amount of revenue your startup makes while making your users feel guilty while using your app, this is a great way to do it.
But give it a try. By the way, the reason Wikipedia has a donation system instead of a subscription system is because a subscription system would not make any sense to its mission and the licensing of the data, as well as tick every contributor off. In other words, it's a last resort for a company that already has traction but needs to remain free and cannot place third party ads on their product.