It would be great to be able to add several products to a collection and have the ability to add individual products to the cart or add all.
this is a great idea. you could just make an extended taxonomy (with pods) of the products, allowing products to be added to any "collection" taxonomy you create. then use a plugin like the purchase visible plugin. (this is what I did).
but I agree. collections should be a part of woocommerce -- it helps with marketing -- you could send out an email and include a "holiday home bar collection" full of things like christmas themed shakers and mudders... things you wouldn't necessarily want to set aside in their own category or things that are too vague for tags?
I'm currently using my custom taxonomy for this purpose, as well as to set aside a section to include a custom header graphic, etc.
hope my reply makes sense.