How is All Saint's Day (November 1) observed in Rome? Would it be interesting to visit the churches named after the saints on this day or would we just encounter huge crowds?
It's a holiday. Unless you plan on going to Saint Peters you won't see much of a difference in crowds, but you will encounter many pilgrims at St. Peter's for the mass. You are spoiled by choice as far as what churches you want to visit, as almost all the churches in Rome are named after saints.
We were at the Vatican on All-Saints day. The museum/sisteen chapel were closed but the Pope spoke from his balcony above the square so it was special in that sense.
There was also a pretty major mass inside St. Peters just before the Pope's address.
On Halloween, there was a parade of primarily American tourists doing a costumed pub-crawl. We joined in for awhile before heading back to our hotel.
People do take all-Saints day off but probably not enough to notice a lack of food or other services.