I'm going to say it depends on a lot of things.
Like John said, finish does play a role, but I think the most important factor is the car, and its style. If your building a G-Machine, more business looking car, then the rivets fit the look. If your building a smoothed out 55 chevy in turquoise and white, then deleting the hardware might be best.
A good example is MuscleCarJohn's 69 camaro with the Super Spokes in smoked titanium. That car, being lowered, and looking ready for the track, looks perfect with the hardware. As does Kenny Davis' Camaro with the brushed Rated X's.
Also, cleaning around the rivets is really not that hard. If you wash your wheels with a lot of soap, and a lot of water, and a soft micro fiber mit or wool mit, all the dust that collects around them will easily wash away.
When polishing your wheels by hand, or with a PowerBall, spray the wheel down with quick detailer to wipe it clean, and any residue left in the nooks can cranny's will easily wipe away.
It's all in the technique.