While I do not disagree that some people can abuse drugs I find this can apply to almost anything in life. People can get addicted to the endorphin's one gets from exercise, or the adrenaline one gets from performing risk taking activities.
I wouldn't say any of these things enhances creativity there have been some studies that show beer help enhancing the persons ability to laterally think. While other drugs like coffee/caffeine assistance help stay focused on a task.
Perhaps it is down to person perspective largely and I think it is unfair to say that all people who take drugs are loser wannabe's and wasting their money.
I say, people have free will, and whatever they choose to do with that, is their choice. Assuming they are not harming any other people of course.
There are many theories that psyclobin (magic mushrooms) assists people with depression and other such issues as it fills them with a "spiritual" feeling of wellbeing and happiness even after 1 "trip". However this would not hold true for all people I am sure.
Others would have a "bad trip" and it would mess them up further.
I personally found inspiration for a book one night long ago while toking outside and staring up at the stars. Never finished it mind... but that was even when sober.
I find that a lot of modern lifes "advances" tend to kill off creativity if you get addicted to it. TV, video games, movies, facebook, twitter, smartphones in general etc... the list goes on.
I think that creativity will find a way, if you are that way inclined. Whether or not you are sober or not. Some people being in an altered state of mind may think of a brilliant concept/idea that they might not have had given the same situation, but sober. Sometimes it is just having the time to stop and let your brain have 5 minutes to go off on one. Whereas a sober person would then start thinking of all the jobs they had to do.
Of course all of this is just my opinion. And may only ever hold true for me within the confines of my own little reality..... and I write all this while on my lunchbreak and watching tv on my smartphone next to me.