This 2004 Cadillac XLR shares many elements of the Corvette C5 and C6, which hides under Cadillac's Art & Science design language. Under the hood the two start to differ, with the XLR using a Northstar V8--here in 320-horsepower guise--and no manual option. The XLR also employs a trick, retractable hardtop. Values on XLRs have remained relatively flat according to Hagerty, with a No. …
