Which if you had the choice or 2 nights in one and one in the other or is 3 nights too long in Sooke we want to take day trips from there.
3 days is not too long at all. You can take a drive up to Botanical Beach to check out the tide pools (check for when it is low tide before you head out!). If you were up for it, you could even keep on going all the way to Cowichan Lake, to Duncan, then back to Sooke, having made a big loop.
There is the Sooke Pot Holes for a cool dip on a hot afternoon too. Or not so hot afternoon... what time of year are you considering traveling?
For hikes, you can do parts of the Juan de Fuca Trail. China Beach, Sombrio Beach, even stop in at French Beach. No trail access from French Beach, but it is still nice there.
I would choose Point No Point hands down for my vacation. (Though I would definitely try and fit in a meal at Sooke Harbor House). I love the privacy of PNP and its quiet, natural setting.