That said... the pop-up window could make spell casting very cumbersome so if they did this, it'd be nice if they made it "smart".
Things like:
- do not show if there are no spell slots of a higher level available (either because you've used them up or the spell uses your highest level spell slot already)
- do not show if it makes no difference to the spell (e.g. Mage Armor, which is always AC +3 for 8 hours even if you use a 9th level slot)
I'm going to disagree with both of those in part, and explain why
1) Disclaimer: This one might be us imaging the interface differently, we could be thinking of the same thing.
You should show all the spells levels, but if you have no slots of that level, the option is greyed out and unselectable. If you, say use up all your second level slots, and just simply remove the second level from the options, there could be a problem of wanting to cast at second level, but forgetting you used all those slots up already, so you accidentally pick the second option - which is actually third-level because the secdond level option was removed - and you unintentionally cast at third level.
2) Sometimes you're out of low level slots and need to use higher ones even if it makes no difference. The problem you describe can be solved by tooltips explaining what casting at different levels of the spell effects, so you can see that there's no difference between the slots at a glance.
