My currently operating Doodle Bug has the stock setup (stock muffled pipe box), for the most part, on a 212 Hemi Predator, and is not very loud. So, riding at night, which is pretty much the only time I ride it, is not an issue. I've left the engine mostly stock because, as it is, the bike is plenty fast. I've gotten it up to 30mph before running out of runway, so it may go just a wee bit faster.
Another consideration is that the bike is, well, about the dang SIZE of Doodle Bug, so achieving wind-burn speeds on it is NOT a priority. While we all know that 30mph ain't that fast - I can drink a six-pack faster than that - on the back of a "Roly Poly," 30 feels like 90 when I'm on my Harley. True story.
I should also mention that, having ridden horses (since I was 2) and motorcycles (since age 4), I've had my fair share of bad accidents (shattered knee in a rodeo and broke my C1 and T4 in Baja, MX on my XR600R, to name a couple), so I'm not looking to trade my two-wheeled toys for a wheelchair!
That said, the Bug will be my quiet little neighborhood cruiser. I am in the process of transforming a Murray Track 2 into a Ratrod style bobber/chopper and plan to eventually put all the mods on it, so it'll end-up being faster, but I'm mainly going for the louder sound to "fit" the look of the finished product.
It just occurred to me WHY a couple of my friends always ask me, "Is this gonna be a long story?" LOL