On two points discussed here:
1. I think rotating-through-spells-assigned-to-mouse functionality would be immensely useful for those of us without a fifty button mouse but only if it's manageable. Certainly cycling all the spells through all the mouse buttons is completely mad. I'd be in favour of simply cycling through spells assigned through some selection - modifier-key clicking on the spells in the inventory, in the order desired, with a special border colour and a wee number in the corner to indicate their position in the cycle, would be enough - and only cycling one of the mouse buttons.
You might even be able to relatively simply allow the user to configure a whole bunch of spells to cycle through a whole bunch of buttons, if there's an elegant way to display that on the inventory GUI - although that might be a bridge too far without a bespoke GUI for the purpose.
In its simplest form, just being able to assign these five spells to my middle mouse button, and to cycle up and down through them using the wheel, would make the whole experience much less fiddly for me.
2. Monster spawners. I'm all for respawning monsters but there is definitely some tedium here at the moment. I suspect much of it is because there's zero incentive to kill the vast majority of them. It feels like you've accomplished absolutely nothing. Less than nothing, actually, because you've wasted magic to do so. This is less prevalent if I up the difficulty or go somewhere more challenging - but then the fact they respawn so frequently without respite isn't tedious, it's annoying.
I'd be in favour of being able to destroy monster spawners for a particular chunk (with a new sort of spawner, or new flag on a spawner for those situations when destroying them would break the gameplay) and then the spawners could respawn when the chunk reloads. Since there's no reason ever to backtrack through buildings and such, this could remain true for dungeons also - or perhaps just until you get x distance away (two rooms, for example).