No it's not too much to ask for. But if you want a girl who's intelligent then expect her to be your match. Some men ask for intelligence then they don't like it and are intimidated - it depends though - higher I.Q is different from emotional intelligence. I have no idea what you're like with women but if you want an intelligent woman be prepared that she *might* be more demanding and won't stand for bullshit.
It sounds like to me that you might prefer dating women in their late 20's or over 30 years old - why not try it?

Depends in which circles you socialise in it might be difficult to get someone who's drug free

Unfortunately that problem is getting more common now.
Confident in which way? Socially confident? A lot of women can vary in this - unfortunately my experience so far has made me think that a lot of women are riddled with insecurities - mainly affecting body image and social issues. Someone could could be vain, look like supermodel and seem confident, but she might ring you if you're out of the house for more than an hour to snoop on you becuause she has issues.
Quote:
I'm simply not digging deeper into my targets, or there's something with my standards that's holding me back.
I'm trying to read between the lines here, becuase I obviously don't know you personally so I'm going to make some asumptions now.
The sentence quoted above reveals part of what you're doing wrong. In my eyes, your standards are at odds with your behaviour - so yes your standards are exactly what are holding you back - but not in the way that you initially thought they were.
Digging deeper into your targets? Consider what you just called your potential casual date or new girlfriend - a target. If she is your target does this mean that she is your prey, or victim then? LOL!!! ;p Do you think an intelligent girl with be ok with this?
Again, I don't know you do I can only make presumptions. But if you expect to get a girl with all the qualities listed above, you might first need to change your approach, or behaviour.
This is a different situation from yours maybe, but a male friend of mine loved mature women - he said he wanted a woman who was strong, independent and confident. BUT, he always played mind games and tested them - like he wouldn't phone them for a week and a half to 'test' them, to see how they reacted. He would be demanding and obsessive when they didn't want to spend every day with him. Then he would come complaining to me saying he couldn't find a woman who was strong and confident.
My reply was that he's probably found plenty - the ones who all dumped him!!! The women who waved goodbye when he did his childish 'tests' on them. They could see through his behaviour straight way, and didn't want to be a part it.
The qualities you listed are very realistic, but are you looking in the wrong places? You might want to branch outside of your social circle or try different settings. For example, if you usually meet girls in loud clubs who like to party, have to tried to meet them in coffee shops or cafes?