I have found a couple things...I'm sending them on, hoping they may have a clue for you........ A Bucks co will;I inlcude it simply because of the names, including a Mercy....maybe it'll fit later.
Page 427. John Smith, Plumstead Twp., yeoman. 3 mo.-11-1801. Proved December 30, 1802.Son William and dau. Esther Smith exrs. Daus. Elizabeth Shaw, Martha Cooper, Ann Fell and Esther and Mercy Smith.Wits: Josiah Brown, Joseph Stradling, Joseph White.
I checked wills, looking for anyone named Mercy, in that area, hoping to find her in the will of a parent, but no luck on that.
I have the Births and deaths of the Wrightstown mm...it contains this..so, you do need to be looking for other Wrightstown MM records...they may have married there.Have you checked in at the Quaker rootsweb list, to see if anyone knows if there are extant, published works on the meeting records.
Children of William Smith and his (second) wife, Mercy: Jos. Smith b. 1st day of 11th month, 1721/2; John Smith b. 15th day of 11th month, 1723/4; Ralph Smith b. 28th day of 8th month, 1725; Esther Smith b. 11th day of 9th month, 1727; Elizabeth Smith b. 10th day of 7th month, 1730; Samuel Smith b. 23rd of 8th month, 1733; David Smith b. 25th day of 2nd month, 1736.
I also found this; Wm Smith HOuse...added to the historical list 4-13-1977 Mud and Penns Park Rd Wrightstown
Are you aware of this book? Smith, Josiah B. (1883) Genealogy of William Smith of Wrightstown, Bucks County, PA. Newton, PA (that sure sounds like a book you NEED.....try antiquarian book sellers.If you tell them a title, etc, they'll be on the lookout for you.....I did that 10 years ago, or so, and found what I was looking for..worth a try)
There seem to be lots of things on Wm Smith, on the internet....have you explored them all?There were several that took too long to load, so I didn't bother, but you should.Try varying your subjects, such as "William Smith"+Wrightstown Bucks co pennsylvania "William Smith""wrightstown pennsylvania +historic building You'll probably get different 'hits' with each different subject.