Herr Hastreng, there's absolutely nothing wrong with running 8" Campy's with stock-sized tires on both front & back. An 8" on the front is a direct bolt-on and eliminates the cheaper 7" wheel's scrub-radius drag, so the steering is lighter. It provides extra brake & cornering traction with a 245-50x 15" tire in front. You retain semi-stock 275-55x 15" rear tires (also a direct bolt-on for 8" Campy wheels). Re-alignment is advisable. I did this in the last century without issues & still have the hard-driven car and the (treated) stock wheels 45yrs later.
As for magnesium wheels degrading over time, this is true: Mag' tends to age-harden and get brittle. The simple fix every 10-or-so years is to dismount the tires off ANY magnesium wheel and place it in your home oven. Bake for 3-4 hrs at 275F- 300F and slow-cool overnight in the oven. Then do the next wheel. This is what the U.S Military did on schedule with magnesium wheels on their fighter planes. It relaxes/anneals internal stresses from age-hardening. Works on vintage open wheel racing mag wheels, too.
If you powder-paint your wheels, it's often applied at 300+F. so its safe. The low stress-relaxing heat also turns stock protective silver paint tan-ish, so after cooling, spray-paint the treated wheels argent-silver again for a stock look. No need to remove the discolored underlayer which is stock zinc chromate showing through. Conversely, I have heard of carefully wrapped, undamaged OEM Campys without tires mounted, cracking while stored on a shelf in a protected garage.