The same question could be posed for any number of genetic defects that we can treat. (for example: poor eye sight or diabetes)
Human ability to mask or compensate for set backs that 13,000 years ago would have meant death or decreased chance of offspring, does have an significant impact on the prevalence of these traits in the population today. Good or bad...it is what it is.
While a mother who delivers via c-section is likely to have a daughter that does the same, what difference does it make if we have the capability to preform the delivery?
As for the vaccines...becoming infected by measles does not mean you had a weak immune system. Viruses and other diseases causing agents that we vaccinate against attack indiscriminately. We are not increasing a particular trait for weak immunity by vaccinating an average child that may or may not have died from some disease in an age before vaccines. All we are doing is combating a natural predator of the human species. Therefore we are limiting it's effect on population growth and not genetic strength.
On a related note, just because your parents had a strong immune system and survived a disease does not mean you will. This is because each person develops their immune system in a very complex manner that involves the recombination and splicing of several genes. Each person has unique antibodies etc...The only way vaccination would have an impact is by allowing genetically immune suppressed individuals to procreate. Unfortunately, for the severely suppressed individuals there are many other diseases (without vaccinations) that are ready and waiting to attack their immune system.
This question also borders along the lines of picking who should reproduce....genetic cleansing so to speak...And even that wouldn't work because there are numerous agents of disease or environmental factors that can alter an individuals fitness level.
I suggest the movie Gattica.