Of course, if you have the choice between wearing, say, a solid navy suit and a navy pinstripe suit, you might want to wear the former. Just so you won't worry yourself over the whole "Is my suit okay?" matter. But honestly, nobody's going to think you're some uncultured barbarian, simply because you're wearing a pinstripe suit to a charitable event on a weekday evening.
Frankly, I wouldn't be shocked if more than a few of the male attendees showed up wearing chinos, sport shirt, and no tie or jacket. Because "it said 'business attire,' and that's what I wear at work." Seriously, depending on the nature of the event (a significant factor, to be sure), this would not surprise me one bit - I've actually seen unfortunate stuff like this at various functions. So don't you worry about something as trivial as your pinstripes.