I would do something like:
Tier 0: Free but nag screen and delays in features.
Tier 1: Pay-what-you-like (with a suggested value, e.g. �29) to get features and remove nag-screen (but limit distribution to a scirra site though so that people have to actively consider it), and you have to go through some 'process' and actively type �0.0 for payment if you want it for free, with a note that reminds people that the software is hard work to make.
For Tiers 0 and 1
Cannot publish games unless they're freeware.
Pay-what-you-want payments that are equal or greater than the commercial tiers (e.g. Tier 3, Tier 4 ) grant you that tier license automatically.
Then various commercial tiers as you suggested, but with somewhat higher prices as a result of the above. Indies who are going to make a little money from their game won't have an issue paying �75. People who won't be making money probably in most cases would pirate the software and get all the features anyway. Maybe this way you can convince a few of them to pay you a little, while the people who would have paid before might drop the suggested price.