I was a kid when this came out and I remember thinking how cool Corey Haims wheelchair was and I remember thinking how lucky he was that it would be so cool to have a wheelchair like that. Kids are stupid.
If this film depicted reality, Marty would have been made fun of and treated as though he was mentally retarded. He would likely to be treated more as his mom treated him (the you poor dear/you can't do things syndrome) or ignored completely. People like Tammy's dad do exist, but they are a small minority.
SK very often makes disabled characters that are not realistic. They are either complete victims or they are larger than life as they end up saving the day.
No; being in a wheelchair is not 'cool'.