undoubtedly regular maintenance will improve a bikes performance by allowing you to use it to its full potential. Along with the regular cleaning and maintenance comes the noticing of small problems which can be dealt with before they become bigger problems. The less quantitative measurement of the question are more in mental outlook. In the process of cleaning and maintaining you mentally (unconsciously) remember why you bought the bike, what you were planning to do with it, how much you enjoy riding, a sort of mental bond is re-enforced and besides it makes you bike feel much better.
Incidentally I also believe that mechanical things like children and small animals respond better to care than neglect.
I find my 10 minutes after ride bike check and my every x number of miles regular maintanence a very positive chunk of me time when I can just let the mind go and do mechanical things that give a positive result.
marni
Katy, Texas
Trek Madone 6.5- "Red"
Trek Pilot 5.2- " Bebe"
"easily outrun by a chihuahua."