Jewel of the North
Thanks. Like I said there nothing inherently wrong with doing it the other way, but it would change the nature and feel for magic use quite a bit in many cases. I agree that finding a universal and elegant solution would be best. I'll continue to think on it as well and maybe one of us will come up with a good mechanic.
What if you do not add your proficiency to your spell attack bonus, making it maximum of 1d20+5 (+/- magic items)? In 4e non-weapon attack (implement attacks) did add a weapon proficiency bonus to the attack roll.