I definitely prefer curly koa for eye candy. As to the sound, I think Chuck Moore once said (and I could be wrong as this is off memory) that it is harder to make it sound good. But he certainly does. Also, I notice Kamaka (Jake, Brittni), KoAloha (Daniel Ho, Herb Ohta, Brittni's old ukes) and Kanilea (Aldrine) all have very curly koa wood that sounds fantastic. So I would argue it does not mean that it will sound bad.
And my skills as a player will probably never be good enough to make a difference between a "good" sounding straight grain and a "lesser" sounding curly one, so I prefer the curly. I actually just special ordered a curly koa uke this past week. And I know the maker creates amazing sounding instruments. I'm not too concerned since the curly koa we chose was from their custom order and high end (not standard production) stash.
It may not be worth the extra $$ but it is personal preference. I have never heard a bad Moore Bettah and they are almost always super curly. I also think Aldrine, Jake, Brittni and Daniel's ukes sound pretty good...all curly.
It definitely doesn't mean it will sound better (might sound worse than straight grain depending on who makes it) but I think it also definitely does not mean it will sound worse or else why would all those pros play curly ukes?