I agree the problem is crits not feeling special, but truth is spellcasters attacks almost all scale with level.
so its not 1d10 versus 1d10 spell vs weapon, after 5 its usually 2+d10 vs 1d10 on weapons. basically spell attacks are designed to get more damage dice. The 'critical' of spells is rolling well on many dice. In the current game crits strongly favor magical abilities, the meta for effective crits is to build large dice pools.
they could give spells a single extra die on crit, but would it even be noticeable as a crit? with say 4d6 versus 5d6 the luckyness of the rolls will tend to outweigh the criticalness.
the problem I think is the psychology, will rolling a 20 still feel great if its fairly weak? This is probably why they are making crits give 'inspiration' The big deal becomes the ability to force advantage or disadvantage, which casters can use to weaken saves on most their spells.
but will a delayed use of inspiration create a great enough feeling on rolling a crit?
