In 2008 69.9 million people watched the VP debate.
Because they wanted to watch Sarah Palin trying to speak in complete sentences. How many based their votes on the debate?
Most polling and assessments have shown that Palin
as a whole had a fairly minimal impact on the presidential race, regardless of all the sound and fury that surrounded her. Despite her 'losing' the VP debate by pretty much any measure
the presidential race polling actually closed by 4 points that week in favour of McCain/Palin. Her favourables enjoyed a bump as well (bigger than Biden's) which ended up not helping her at all at attracting voters that McCain himself wasn't particularly popular with. Taking
this analysis she only actually mattered to Democrats;
The results of the analysis are quite distinct for the three groups. For Democrats, evaluations of the four candidates all had statistically significant effects in the expected directions: higher thermometer scores for Obama and Biden decreased the likelihood of a McCain vote, while higher thermometer scores for McCain and Palin increased that likelihood. For Republicans, the opposite was true, as evaluations for only Obama had a statistically significant (negative) impact on the likelihood of a McCain vote. For Independents, strangely enough, only the evaluation of Palin failed to exert a statistically significant impact.
They later note that she did have some impact with white independents, but that this is a marginal effect at best and those results quoted show that the other candidates had more significant impacts with independents as a whole.
The VP choice can help frame debate issues and flavour the campaign to a significant degree, but beyond that the VP themselves are of fairly little importance as far as votes go, and the debate itself is a sideshow and good entertainment at best.
The Ryan pick is important as far as it shows Romney doubling down on a conservative, regressive tax ideal.