Increasing the CR of Spell / Magical Traps

[Mavrickindigo]

So, I'm looking at the SRD for how to determine the CR of a magical trap, and it seems like the CR is either equal to 1+Spell Level of the highest spell or 1+1 for every 10 points of damage it does on average.

I'm wondering, then, how to make spells have a higher CR than the spell would allow. I mean, mechanical traps have a ton of modifiers that could be applied to them, but magical traps only allow a choice of 2 modifiers?

[CampinCarl9127]

Increase the DC, add extra abilities (maybe that electric trap also has a paralysis or a stunning effect), increase the range, add metamagic to it...the possibilities are only limited to your imagination.