From my experience, I would argue that weighted GPAs are inimical to both students and colleges seeking to evaluate them. I've seen that the desire to gain a high weighted GPA often leads to drastic measures to game the system. These include things like refusing to take things like Band because they are not weighted, and therefore will dilute a high-achievers WGPA. Also, students tend to systematically identify "cheese" AP classes such as Psychology, Government, Statistics, Economics, etc, and take them even if they don't care about learning the subject matter.
This is a common occurrence, even in standardised testing, but there's two sides to it.
A really high achiever here will take one of the following sets of subects:
- English (Advanced, or Extention levels), Extention 2 Mathematics, Physics, Chemistry, [Other]; the other won't be counted, but the rest are generally the most difficult courses and hence for good students, will give the best returns on their time investments.
- Extention 2 English, L.O.T.E x 3; these are typically people who have both good linguistic skills but also speak one of the Languages Other Than English at home. French/Spanish/Italian is a common triplet.
So certain courses become really popular, even among people who are going on to completely unrelated degrees, because they score well (if you're good).
However, the flipside is that a number of people will do courses that are too difficult for them, because they think their marks will "scale up". Out here, we don't scale linearly, we scale against gaussians (bell curves). You only get scaled up if your position on the raw mark distribution is higher than the crossing point of the raw mark distribution and the normalised distribution. If you are in the overlap region, your marks won't change much from raw, and if you're in the tail end you will actually be marked WORSE than your raw mark.
Getting above average in the lower course CAN (and often is) better for your grades than getting poor scores in the harder course, which is why it's so important to pick courses appropriate to your aptitude level, but very few students understand that.