It's a given that we are voting in theory for candidates and not the parties they represent but in practice this is not what happens and indeed most people know this. Hence the campaign is framed in large part in national terms.
Hence, I think that dismissing voting reform because "that's not what we are actually voting for in an election" is missing the point. Should local issues really be such a significant part of how we elect our national government? For many people, the answer is no -- and hence the need for electoral reform, because FPTP locks in the answer as "yes". It might be nice to stick it to Ed Balls or Michael Portillo or goodness knows how many other high-profile people might lose their seats, but the end result is that the make-up of our national government is often heavily influenced by small local swings. Hence the focus on key marginals, etc., that mean that large parts of the country can just stop mattering to the people in power. (Well, usually, Scotland being an exception.)
Ultimately electoral reform is not just about the system by which we choose our MPs (First Past the post or Borda Count or Alternative Vote or Schulze method or whatever), but also about what we are choosing our MPs to do, and the reasons we are electing them. The current system doesn't just disenfranchise a sizable proportion of the country, but then also turns people off politics, and allows for a certain type of politician to make it to the top when otherwise they would not. A change to the voting system would help to address some of these issues, but has to be part of a larger change in the way our country is run.