There's some crazy people in this thread.
The only real point I want to make is that (it's probably been mentioned but I don't want to sift through 369 pages) in general, transportation backbones which the Skytrain lines qualify as, are not built just for density especially residential. They are also built for the 'working man' trying to go to work. So you can't simply say:
"Well the Broadway cooridor is high density so it should have a Skytrain line." This is why project studies aren't done in 2 days like some people would like them to be done in. When you are looking for new lines and planning transit maps out you have to look at the entire picture including the destination, route, and where the origin is.
So the UBC line wouldn't be built for the Broadway cooridor, it would instead make sense to go along that route to help out and or give alternatives to people living there. The reason it would be built though is to get the workers and students to and from UBC from other parts of Metro Vancouver much like the line out to YVR is meant to help the 20,000+ workers that commute there every day even though Sea Island has a residential population of next to nothing.
For UBC alone you'd have to correctly sit down and look at where the student and worker populations originate from. If for example you have 20,000 students at UBC but 10,000 live on campus, then you can't say "look they have 20,000 students!" when it comes to transit, you have to take the lesser number because those living on campus students will spend most time there and don't fully qualify against the equation. Same with workers. If you simply go 20,000 people work on campus you have to figure out where most originate from. If 10,000 live south of the fraser and you build a line that links UBC to North Vancouver (as has been mentioned), will that help? Probably not. Same deal if you build a skytrain extension but for those people living south of fraser there is no effective way for them to get to skytrain in the first place, then again you aren't solving anything. If it turns out 75% of the people at UBC live on the broadway cooridor then there is a good argument. Not to mention you don't have a solution that involves telling people "Well move closer to Vancouver" since the bulk of people in Metro Van live 'out of town in the burbs' so those living 'in town' are actually the minority here.
Same thing building a line anywhere. Would you build a high end line down a road cooridor with a lot of restaurants? Or would you build one down a cooridor with a lot of destination stores and office locations? Even if there are way more restaurants on the first road? I mean the map may show more businesses and jobs there. But they are restaurants so the commuting footprint is far different than office space.
Again this is why transit studies take years and you can't just look at a single table of numbers of a fancy colored map of metro vancouver with population densities.
UBC is a major destination, South of Fraser including Langley is a major Origin as is Coquitlam. That means while UBC is important it isn't for sure more important or less important of those other links getting transit alternatives. Is Skytrain the solution? I don't know for all.
I do think though UBC needs a rapid transit link that aren't busses. Makes sense. But I think 1 can't happen without finally getting that bloody Evergreen line done AND increased transit options for people South of Fraser. Not to mention more focus on better densification and people not needing to commute 60km to and from work.
But yah don't just say "WE NEED X CUZ HIGH DENSITY LAWL." because that's just silly and missing the big picture.