You will want to regroup.

Lighthouse: no, no and no. It is isolated from surroundings, no lighting, dark and not particularly safe for staying on the trails/not falling into the water. Nothing to see at night there.

Seawall: which one? If you mean the seawall in West Vancouver between 17th St. and 25th St. Yes, depending on when you are coming here. Until the end of August, the sun will go down about 9-ish, but there are street lights along the way and probably other people. Very nice to look out over Burrard Inlet and Stanley Park, as well as further over to Kitsilano, Spanish Banks and Point Grey.

There are also seawalls around Coal Harbour (okay), False Creek (okay) and Stanley Park (maybe not). English Bay has a nice sea walk all the way up to the Burrard St. Bridge.

Lynn Canyon: ditto no. It is all forest and trails, no lighting and tricky in the dark for footing and physical safety. Nothing to see at night there.

Safety is a relative thing and is as much about luck as it is about planning. You can have a perfectly safe walk through the worst part of town, or be mugged in the best neighbourhood. There are no boundaries to crime. Clearly, there are things you can do to manage the risks, but I don't think it's legitimate to classify one place as "safe" and another as "unsafe". It misrepresents the reality that you must always be on your guard, but at the same time, don't allow fear to dominate your thinking.

Overall, Vancouver et environs is very safe. Lately most of the crimes have been targeted hits against people who are involved in that lifestyle.

However, considerations of lighting, wildlife, gettting lost, etc., are valid safety concerns when venturing out into parks, especially alone. Try to use a check in/out system with someone (like hotel staff, or even someone back home you can call to check in) who can follow up with search and rescue if you do not return on time.