If you are looking for salmon runs, I'd skip Newaygo and head to Baldwin without question. The Pere Marquette is one of the best, (some will argue the best) in the great lakes. All fish are wild/strays and numbers are fantastic. The great lakes salmonoid fishery began in the PM if yer a history geek. Within a half hour or so you've got the Little & Big Manistee, Bestie, White, Pine rivers.. although the PM can take up a weeks time.
The Muskegon river in Newaygo isn't too far away. It does get salmon runs but is not surrounded by the outstanding rivers in the Baldwin area. Newaygo is more of a modern town and there's not much to do in Baldwin, but fish.
I have stayed at Baldwin Creek Lodge (http://www.baldwincreeklodge.com/trips.htm).. Mike is a nice guy, knows his stuff. A little cocky I suppose. His place is nice and cozy, right on the baldwin river. Not superb accomandations.. just a lodge for fisherman. Cheap.
Betts Guide Service has got a great reputation for the area. They fish the Muskegon and PM as well.. everyone I've had talked to recommended them. I have never talked with them.
I've got a few names of guides that you may want to stay away from. I can explain in PM if you feel its necessary.
I was there in fall. I've always wanted to go for the spring manistee run on the PM but it's hard to justify passing up Ohio's manistee to drive 6 more hours.
I actually spend most of my time in southwest Michigan/Northwest Indiana for the summer steelhead run. Sometimes we hit up the PM and surrounding area while out there. The PM gets a few fish in August and the little manistee gets a July run of kings.