I always tend to look presentable for religious occasions. I wouldn't call "chuch wear" dressing up, though, since it's just the observed decencies. You just want to look like you take your appearance seriously on those days.
And as far as men's wear goes, I really hope that we get over this trend of calling a suit and tie "formalwear"--they're not. They're lounge suits, and they are informal by definition. Heck, even morning coats (which, as part of morning dress, get lumped in as "formal" or "full dress" along with white tie for eveningwear) isn't really fully formal, since frock coats are. Although that might be excessively pedantic: morning dress and white tie certainly qualifies for state occasions, whereas nobody wears frock coats (or still more absurd: knee breeches of levée dress, likely last seen at the coronation of HM the Queen.)
So to conclude: boys, wearing a suit and tie is pretty much a basic decency and really ought to be considered the minimum appropriate attire for family occasions, etc. What a time we live in, eh?