Yeah, I didn't go for the take it out of the box and make it like the picture stuff. Like you say, takes the whole point of them away... creativity, building design skills, etc.
HO was my thing, too! My favorite piece of track was the train crossing with the road. I had quite a layout, scenery, buildings, static cars & trucks and all. This was in the mid-late '60s. I wish I had all those cars now.
I remember I got a hold of some phosphorescent paint. I painted the headlights on the cars and ran them around in the dark. Then there was souping them up, spongy slicks you had to carve out the fender wells for. Did you ever cut the chassis out so you could put a second magnet on the back side of the armature? Yeah, would burn out the armature before too long, but they sure ran like a bat out of hell for a while!
How about making then to do wheelies? Let's see, you'd glue the springs to the chassis, cut the shoes up front so they didn't click onto the tabs, hold them spaced with electrical tape with the pin in between. I had a drag strip with a pillow at the end, do wheelies all the way down the track on the ones that had the extra magnet.