I know one guy who has on occasion parked at a business in Cascade Locks because he said it was safer for his car. That adds 2-3 miles to the hike, and I think is pretty extreme. I haven't hiked the trail 75 times, but I've done it many times with no issues.
Just want to be sure you understand that 7.5 mile is not a "campground", it is an area along the trail with a bunch of backpacking campsites, some nearer the trail, some nearer to the creek. It is one of the few places where the trail is not right above the creek. There are a few sites within the next quarter mile and then sites get pretty far apart.