Roofing Flashing & Ventilation questions

I'm in the contracting phase of a roof strip and replacement job for my split-level house. The shingles will be the architectural type, either by GAF or Certainteed.
My leading proposal has specified shingle valleys. Aluminum flashing is also available. Are shingle valleys as watertight and long lasting as metal flashing?
The roof currently is ventilated by gable vents and there is no ridge vent. I have specified that a ridge vent be installed. The existing soffit vents are circles only about 3" diameter spaced every four feet. I think we need better soffit venting.
The contract has an option for air vent ventilated dripedges. Is this worthwhile, or would merely cutting in more (larger) vents work just as well?
Any advice for roofing work would be much appreciated! Thanks.
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scribbled this interesting note:

A properly installed closed valley will last as long as your roof will last.

You are correct. You need additional soffit vents.

I've seen but never use the ventilated drip edge. I don't like the looks of it. Seems to me that it would require frequent cleaning to clear accumulated dust. More soffit vents or even continuous soffit vents would be better.

Hope this helps.
-- John Willis (Remove the Primes before e-mailing me)
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Shingle Valleys IF installed (woven) properly, are great. If not interwoven, they may reek.
The ventilation system should be designed holistically so that air movement is proper. Are their airflow problems currently ?
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