It's not that the responses are not accurate: they are. But they do demonstrate how (as usual!) I am the odd one out in these discussions, and on these occasions.
First Communion was a pretty intense day for me and for all those who remember that day, that I can think of. I, and all I know, preferred a traditional look not because it was "bride-y", but because it was formal and tasteful. I've seen some modern 1st communion events. What strikes me is not the particular style of dress, but the particular lack of care in presentation. This is not a matter of money but of grooming. For example, recently I was looking at 1st comm. photos of a parish I know. I didn't see the boys; maybe they looked better. But the girls looked "thrown together." Straggly hair, sandals instead of shoes, and just very little care (a task which belongs to the mother to oversee). And yet they were all wearing white (& various kinds of headpieces -- some veils, some not). These were not poor families, either.
I don't expect modern girls necessarily to go to the extent that my own mother did with a pin-tucked hand-made organza dress & custom petticoat & white gloves, but on modern girls I would prefer to see more care in however they present themselves, including if it's a simple outfit as described in some posts above.
For the record, my own daughters did not at all look "bride-y." They both had unique white dresses which were adapted from previous uses and then later, for following uses. (In line with some of the posts above) Yet they definitely fit right in & rec'd compliments on the taste shown. They did not wear veils, but flowers that coordinated with the dress. So in other words, they were modern. Perhaps the difference is, I insisted on grooming & appropriate shoes.
It's a special once-in-a-lifetime day. Appearance is not the focus, but neither is appearance inconsequential to the sense of specialness, i.m.o. It's just part of the care one takes, whatever the budget & whatever the style chosen.