All good points however usually with the free version on the update all of the content previously locked behind the paid version is then added to the following free version in the next update. So as an example all of the paid content in 04 would then be free in 0.5. This is pretty much the standard has how to most creators use paid demos or updates involving Patreon. Beyond this another reason people are disliking this payment plan about paying for each demo is that you do have a Patreon, one where you are already having people pay in order to access the game early. While I could be wrong I haven't seen a single other creator with one also have paid demos, at most they have a one time payment to access the game or have the non patreon version free but locked to one update behind the patreon, sort of an incentive to join.
So to answer your question there's three possible methods you might want to consider (though other users might suggest others):
1. Stagger the updates so the patreon has access one month in advance of all other sites. This will incentivize people to join the patreon in order to access the game early.
2. Have people pay $10-20 for access to all paid demos but also include the staggering idea in option one to further entice potential buyers while also giving another option on how to access the game.
3. Have people pay $30~ upfront but also give them the full game for free upon release as an incentive for them to buy it early. (Allowing people access to the final version for free would also be an amazing offer for higher tier patreons as it is once again another incentive for them to give money on a monthly basis versus a one time fee)