A good point, but I think it is born of the same idea, if your spell is easier to cast, you will commit fewer PD. Extra PD means more spells to cast. Everyone expects some of their spells to be dispelled every round, many magic phases are such that as a defender, you can surely dispel one spell, or take bad odds on dispelling two spells (or something similar), so most people seem to just throw it all at once (remember, if they fail the first one, they cannot use that caster again to dispel that round, so they take a -2,-3,or -4 to dispel attempts).
The most important aspect of the +1 is to not lose concentration. I will admit though that there are times that there is a discrepancy of 1 between caster and dispel roles, they seem to be uncommon. The extra power dice from a staff/HC combo will likely cause your opponent to act irrationally, realizing they are outgunned in PD, and blow their dispelling potential early leaving you an open field to cast as you please.
I just dont like the book taking up so many magic item points that I am left to choose other mediocre gear.