Crazy Jerome
First Post
If they're going to do that, why not just have spell points instead of spell slots?
Same reason why Arcana Unearthed/Evolved did not--spell points have their own problems, and contribute even more to "wizard with massive flexibility always having the right thing at his finger tips and thus overshadowing those will skills" or "wizard pumps all of his points into massive damage and has nothing left, party rests."
AU/AE isn't perfect, but only being able to trade up or down by one spell level is a powerful constraint over the usual spell point system. Or to use economic terms, spell points are entirely fungible, while even flexible slots are not.
That is, say you still have slots available to cast 1st through 5th level spells. You break one of your 4th level slots to get extra 3rd level slots. You can't turn those 3rd level slots into even more 2nd level slots, but you can turn one of your existing 3rd level slots into 2nd level slots. So for you at that moment, everything is totally fungible, and just like trading in a 4th level spell for a bunch of spell points which you use to buy a boatload of 2nd level slots. However, the caster has to be careful. Once you are out of 3rd level slots, you can't do this anymore.
The net effect is that of a spell point system where each spell level has a limited number of points allowed, well shy of what your spell point total would be. How many 4th level spells can you cast, total? The number of your 4th level slots, and then any weaving you can do from 3rd and 5th level slots. It is a more serious restriction in play than might be apparent from a casual glance.

Also, the ratios for trading up versus trading down are different. This is transparent and easy to manage in AU/AE, but would be somewhat annoying in a pure spell point system.