Here's my experiences with these subjects:
Skyline:
Any tall building along the west Broadway corridor would be good, 805 west Broadway, this building:
Frank Stanzl Building by
entheos_fog, on Flickr
is the tallest and I've been to the top floor and the view is amazing. Ugly building though.
7th Floor of BC Cancer, anyone can just walk in but you'd need to get higher up:
134/365 - Vancouver by
entheos_fog, on Flickr
There's lots of good vantage points in Fairview as well, you won't get as high up, but any roof without trees in the way would be good. Here's a few non-roof top skyline shots frm Fairview:
332/365 - Vancouver Skyline at Dusk by
entheos_fog, on Flickr
Buildings are in the way, but you get a good idea of buildings you could try out:
Downtown Vancouver Panorama by
entheos_fog, on Flickr
QE park is ok but the trees get in the way:
Vancouver at Dusk by
entheos_fog, on Flickr
And then there's this view:
277/366 - The View Up Here by
entheos_fog, on Flickr
from the King Edward Village condo, top floor. But you gotta know people
And the vantage point from here in Burnaby is quite stunning, too:
Vancouver, Looking West by
entheos_fog, on Flickr
And then there's always the views from Kits, Jericho Beach being a wise area to shoot from:
Lifegurds, Beach Goers and City Views by
entheos_fog, on Flickr
205/365 - View=Ruined by
entheos_fog, on Flickr
Or Dunbar:
Downtown From Afar by
entheos_fog, on Flickr
As for autumn colours, 11th avenue in Mount Pleasant is a great street when the leaves turn red, I think it's close to Ontario street. The whole block is like this:
Autumn in Vancouver by
entheos_fog, on Flickr
Speaking of Ontario street, these pointy trees go all the way down to 2nd ave and turn nice colours, too:
Autumn in Vancouver by
entheos_fog, on Flickr
But just walking around any neighbourhood is a good idea, you'll never know what you may find!
Kitsilano Street by
entheos_fog, on Flickr
Hope this helps