I'd never get one signed. But I have purchased one that is signed ( Lando Skiff - Billy Dee Williams ) and I love it much more than a plain Unsigned MOC - and I have a few Lando's !
Ultimately it's going to be up to the individual. Like all things when you sell it, the buyer is going to pick holes....if it's creased, yellow, faded or signed it's worth so very little the buyer is doing you a favour letting you sell it to them....and if your the buyer the creasing is minor, yellow hardly notices, it's only faded in some lights and the signature is brilliant and increases the value.....
My point being it is all subjective.
Always buy what you want at the price you want to pay. Forget about the commercial value as that should be sencondary in my view.