Full disclosure: I'm a wuss about heights. My partner wanted to do the elevated redwoods walk at Redwoods Altitude. I was VERY brave and said yes. It was pretty busy for 4PM on a spring Saturday.
From a walking point of view, it was physically easy. Just the walk on its own cost $45 per adult and took 45 minutes to an hour, depending on how long you wanted to linger. You need to be able to handle some stairs. But every redwood platform includes seating, so you can rest along the way.
You DEFINITELY feel the elevation - you are UP in the trees. The swing bridges sway and creak. The wind rustles. The tree bark is rough and fragrant. You are indubitably far away from the ground, and how you feel about it is up to you! There's one section where you have the option to go even further up - the staff described it clearly so I was able to opt out. Whew. My partner loved it, though.
Once you get beyond the first two platforms, it's pretty hard to turn back - crowd movement is all going the other way. But each platform is numbered near its bench, so you can tell how far along you are. A nervous little kid - or me - can count the platforms and know how much more there is to go. You can also distract yourself with all the forestry information placards along the way.
Even if you don't love heights you'll make it through with a sense of accomplishment. Reward yourself at the gift shop, and maybe go for a ground walk through the redwood forest afterwards.