From my experience, and I am not a PRO by any means... There is never TOO much ventilation in the attic. I dont think you want to interrupt in any way the air flow from the soffit vents through the attic and out your vent system at the crest whether it be ridge vent, attic fan, whirly bird, or side levours cut into the attic walls. If your soffits are wood, then you probably have vent grates in them every few feet. If you have vinyl or aluminum siding then the soffits might be perforated the whole way. If you block the soffits or even constrict the space from the soffit to your roof rafters, I believe you will be putting limits on the natural flow of cooling air up through the soffit vent to your ridge vents which traps heat. In the summer that may limit your insulation benefits.
Personally I have vinyl siding and a very high roof line with a cavernous attic. I can stand in the middle of the attic with the lights off and see a bright glow coming from the soffit area all around. I also can see light at the crest of my roof via the ridge vents. Also light comes in through my two attic roof fans. These areas do not leak in any way and the temp in my attic was only 108 F at eye level on a 98 F August day last summer with my roof in full sun.