I'll be up there the same weekend doing both trails Silver Peak and The Crack. The Crack is nice, but Silver Peaks is just an overall more breathtaking viewpoint. I'd stick with your original plan, and possibly even get an early start on your last day and hike the crack (starting from the highway) and then head home afterwards. Especially since it's Thanksgiving weekend and hopefully fall colours will be at peak, you don't want to skip Silver Peaks.
In terms of campsites, Boundary is a nice site, and it's private (which is great since that weekend will be very busy), but you're right that it doesn't have the traditional Killarney views. If you want a site with a better view, you can try your luck with David Lake, but there's no guarantee you get any specific site and it will get fully booked so you might spend a while paddling around looking. Also there's a couple of cottages on the lake.
Between paddling through the park and doing the Silver Peak hike, you'll be surrounded by the scenery even if your Boundary campsite doesn't have the specific view. The end of the portage into Boundary is a massive rock you'll need to maneuver down, so trust me you'll get your first experience of the Killarney mountains then

Personally, I say stick with your plan, and if it's possible to add The Crack as well, do that.
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