Hi Brian,
I'll save that nightcap for later, it being only 8am in the new time zone in which I find myself today (although I must admit I feel like it's late...) You're right to be sceptical of anyone named John Smith, but you never know...
Somebody has to be the right John Smith! I once thought I had lost track of a great aunt after finding her marriage to a John Smith, but the family had the good sense to move to a village of 60 inhabitants in Arizona and were thus the only Smiths for miles around
When navigating Ancestry.com, do take advantage of the flexibility of the search. If you don't find someone under the right name, try, for example, anyone (name left blank) born in Scotland at about the right time, who emigrated at about the right time-- and you may just find others in the same family! Always start with a wide search. If there are too many results then gradually narrow it down one field at a time. If you still don't find them then try varying the fields you specify. Think of the things that are often mis-transcribed, such as age, which is often off by quite a bit and also place of birth, which the emumerator often puts as the current census state instead of the actual place of birth. There are many fewer indexing errors in the U.S. censuses (they were done before the brilliant idea of using OPR technology

) but sometimes the indexer went cross-eyed and noted down the birthplace of the neighbor instead. Most of the errors, however, are not in the indexing, but were made by the enumerator at the time (or given wrongly by the person enumerated!)
All the best in your further searches

A jetlagged Sarah