I wonder also if the obsession with sticking to the 100/d20 = +5 leads to part of the problem. . . .if the granularity of the bonuses was by +1s then the bonuses would pile up faster. . .since the least bonus is +5, the next is +10 the next is +15, etc. etc.
If your moderately magical sword was +8 and the moderate spell +7 you'd be stacking at +15 rather than the moderate bonus of +15 and the moderate bonus of +15 stacking at +30.