Sorry about posting it here, but the Combat&Magic forum seems to be now only an archive and didn't know where else to fit it.
As a lover of unorthodox combat I've been having this on the top of my head for a while. Things like whether the bonuses from the Shield spell add to enemies' DC of performing Combat Maneuvers on the caster like grapple (it automatically interposes itself between incoming enemies and the caster after all) or whether the enhancement bonuses from a +2 Sickle or Flail apply also to a character's CMB when using the weapon for a Trip attack.
Given how the book doesn't say otherwise I personally say magic modifiers apply but, is there a designer handy just to be 100% sure?