I believe Millers were in fact built in Seattle, but I'm only aware of the later 28' model you described, essentially a 70's racer/cruiser of which not too many were built.
The Quanta was locally (Vancouver) built, and has a great pedigree. The designer is Ray Wall, who, while working with Camper Nicholson in England designed what became the CS 27. He brought that design to Canada in the early 70s and helped form CS yachts. He went on to design the popular CS36 (traditional) and the CS33.
He later (early-mid 80's) started Quanta Yachts in Vancouver and designed the 28, of which unfortuantely few were built but it has many of the qualities that the CS 33 and 36 had and was apparently very nicely tooled for production. Build quality is reportedly very good. I do share your concern about it being underpowered if in fact it's only a 9 hp engine.