Do we need the amy-pond tag?
It feels superfluous.
I don't think this tag is particularly helpful.
As Gilles mentioned in his comment to this question, we've had similar situations come up with character-specific tags in the past, and the most popular answers to the Star Wars and Harry Potter versions pretty clearly establish a precedent for character-specific tags being generally unpopular, and not being perceived as particularly useful in general.
I'd be more inclined to see a doctor-who-companions tag than one tag for each particular companion (because if we have a amy-pond, why not a rose-tyler, harry-sullivan of brigadier-lethbridge-stewart?), but I just don't see it being necessary.
It seems unlikely that someone would subscribe or ignore an amy-pond tag, or that questions specific to Pond couldn't be found using a combination of the existing tag and text searching. There are a fair amount of Amy Pond-related questions, but the ones specific to her aren't a huge proportion of the total Doctor Who questions, and with her exiting the show as a main character, that proportion seems almost certain to decrease over time.
Finally, I fear that such a tag will be used inconsistently. It may not occur to most people that they should specifically be adding such a tag, and there are already questions that would qualify that don't have the tag. This means that in order for the tag to have any value, a significant effort of cleanup for existing questions would need to take place, and users would have to pay attention to any future questions and ensure that the specific tag was added. I just don't see the payoff for this justifying it.
Since I appear to be the one to blame for the tag, I feel obliged to answer;
We have a ton of character specific tags for various franchises and I don't really see the harm in extra tags, even if they don't have hundreds of questions. In this case I think there are some more questions related to Amy Pond that are just not using this tag, so I'm not sure if the two questions currently tagged so are representative (regarding quantity).
Given current story developments I'm not sure how many new Rory/Amy questions we will get but we could retag older questions.