I'm quite familiar with that outbreak.
I really don't think it's reasonable to compare our knowledge and methods for handling a flu on an individual basis to those of 1918. People were dying from dehydration, that doesn't really happen anymore in America.
I don't think dehydration was what caused all of the deaths. Certainly it was a contributor, but I think it caused an over-reactive immune system as well. I think Influenza can cause a variety of symptoms beyond the mildly obnoxious ones like vomiting, diarrhoea, etc.
Regardless of the cause of death, the 1918 pandemic infected up to 50% of the population. I'm not an epidemiologist, but I think that alone is a pretty serious cause for concern. Don't viruses mutate pretty quickly? Doesn't this mean new, more serious symptoms could arise because of this?
I think it'd be foolish to prepare for a disaster right now, but it'd be even more foolish to not take steps that prevent one.