The thing about those caster items (and I think that probably even better than upcast scorching rays is simple upcast magic missiles, if you use ALL the items that add +damage die per missile), is that, well....I kind of think they're a pretty crappy way of balancing casters. They "boost" casters by narrowing the number of spells they have to choose from (because anything other than some spell that has multi-hits becomes a pointless use of a spell slot, except as you mentioned, haste for further enabling your martials.)
Well, magic missiles are indeed strong but the thing is they are force damage, as it is in the game, we have no ways to increase force damage output aside from some items. Also, magic missiles can never crit, they are static damage. Very reliable, but static. Also, magic missiles are useless against githyanki (and enemies who cast shield - and sadly, on tactician they are smart enough to use that reaction if they have the spell available). Now something like scorching rays can miss, yes, but it can also crit. Also, Markoheshkir staff works really damn well with scorching rays - it increases damage per ray and then on top of that fire bloodline increases that as well. Oh and let's not forget the heat you get from using fire spells which you can use to further increase fire spell damage. So yeah, in my case I am better off casting scorching rays that can crit over magic missiles, but magic missiles are the king of early game though.
Edit: But yeah, I agree, items as they are in the game are so damn poorly balanced it's sad.
