Thanks for the kind words, and sorry for the delay in replying -- minor emergency at home (broken dryer).
Anyway, I am also no longer a real mountain biker -- age and sports injuries have caught up with me. We ride mostly on pavement or gentle dirt roads -- no more death-defying single track for me.
In the Humboldt area, the Avenue of the Giants is the main attraction, and it can take a couple of days to ride the whole thing. Start near Redcrest and head up toward Myers Flat -- that way, you have a slight downhill at the end of the day!
Mattole Road is a great ride -- start at the Rockefeller Grove trailhead. As you are driving west on Mattole Road, watch carefully for the entrance to the grove -- it is hard to see. And of course, hike around the grove itself. Ride west from the grove, as far as you'd like.
The Flatiron/Bull Creek trailhead is worthwhile -- in hot weather, you can wade in the creek. The hikes from that trailhead are great.
I'd recommend staying at Ancient Redwoods RV -- it is actually quieter than the campgrounds in the area. If you are there in early August, the blackberries are amazing.
Our favorite redwood park is Prairie Creek, between Eureka and Crescent City. We usually stay at Kamp Klamath RV Park, if we can't get a space at Prairie Creek itself. Kamp Klamath is sort of funky -- the bathrooms are very old -- and some folks don't like the "campground" type atmosphere at Kamp Klamath. (We do -- the sites are grassy and not too close together, and we don't use public restrooms most of the time.)
If you want a fancier RV park, there are several nearby. The drawback is that those parks are much nearer to the highway than Kamp Klamath is.
I would not recommend staying in Crescent City and commuting to Prairie Creek -- it takes almost an hour on a twisty road.
The bike ride along Newton Drury Parkway is world-class -- start at the south end and ride north. Again, that gives you a nice easy downhill on the way back.
Don't miss the James Irvine Trail and Fern Canyon. You can take Irvine all the way to Fern Canyon, but it make for a long day. I'd recommend starting Irvine at the park headquarters and going as far as you want, then turn around.
Fern Canyon is worth the drive. If you can, bring good strap on sandals so you can walk in the water, if the weather is warm. If you have extra time, hike north from the canyon on the Coastal Trail, which is on the beach. If it is dry enough, you can ride it on a mountain bike. If it is muddy, it is too much work in my opinion.
We've been mildly disappointed by the Jed Smith area -- there are not many hikes, and you can hear road noise on most of them, which detracts from the "cathedral" aspect of redwood hiking.
You mentioned crime in Crescent City -- I have not heard anything about that, but like they say, "Absence of evidence is not evidence of absence." I'm not sure what that means, but it sounds wise.
Here are links to four of our blog posts that involve the Redwood Coast -- I hope they are useful, and let me know if you have additional questions!
Look, Mom, We're Camping!: Northern California Coastal Redwoods: May 2021