I recently scored a pair of like-new Allen-Edmonds Broadstreet brown and white spectator shoes on eBay for $68 shipped:
Spectators were originally darker calf and white (or colored, but lighter than the dark portions) suede, like saddle shoes. This provided a contrast not only of color, but of texture.
Will Boehlke and Alan Flusser have both opined that all-calf spectators are worthless, shouldn't even exist, and should never be worn by anyone.
The real, calf and suede version is definitely more attractive and visually interesting, and is preferable when it's available.
However, it's likely to be out of the financial reach of most men. Allen-Edmonds is the least expensive quality shoe brand, and this all-calf version would've been north of $300 at full retail -- and for a shoe that's only in season about 3-4 months per year (either Easter-Labor Day or Memorial Day-Labor Day, depending on one's opinion), and even then is only an occasional shoe. (AE has a custom program for a $100 upcharge, and they might be able to make a suede and calf spectator for that.)
Also, I've seen vintage all-calf spectators on eBay from the 1920s, which is close to the shoe's origin of popularity. This reminds me of Flusser's contention that notch-lapel tuxedos were either invented or became widely used (probably the latter, but I can't remember off-hand) in the 1960s as a cost-cutting measure, because they were made by manufacturers using business suit patterns. However, people have produced scans of clothing catalogs of tuxedos from the 1895 era (about 10 years after the tuxedo was supposedly invented) showing notch-lapel versions for sale.
In my view, all-calf spectators are like notch-lapel tuxedos: less than ideal, and less stylish than other versions, but not deal-breakers.
And even the all-calf versions will definitely put a spring in your step, and will garner plenty of double-takes -- usually followed by longer, admiring looks. So look into getting some for your summer wardrobe.