There are a few games that you might miss out on with this method. Some devs (it’s not many) list their games at what they think is a fair forever price and will not ever offer the game at a reduced price. Again, this isn’t a lot of devs, but one notable one is Wube, makers of Factorio.
I generally agree with your method, mostly because I have a large enough backlog to be able to wait for sales, but it is also worth doing research on some devs to see if a sale will ever happen.
You should see an increase, but likely small. Since the end point increased and since the curve only increases between upgrades, that means that all points before the end point must also increase. However, most of the benefit is now granted in the first half of the upgrades possible, so at your level the increase per level will be smaller than it was before.