Q:

What's the most efficient way to "blank" old comic word balloons while retaining paper texture?

I'm taking very old (1940s and '50s) comics and trying to remove the text from some of their word balloons. I don't want to just erase their contents to pure white space, though, as the paper colour and texture isn't pure white; it's slightly yellowed, and grainy (paper quality back then wasn't great). What I'd like to end up with is something that looks like the original scan as though the comic was never lettered. 
At the moment, I'm trying to find the largest blank space possible inside a given word balloon, copy the best square or circle I can fit inside it, and paste that square or circle repeatedly to cover the text. This is painstaking, and also results in an end effect that's kind of weird in and of itself, as I have the same bit of texture repeating over and over and over. 
I've tried "smudging" results, but that gives me something that's again kind of weird-looking. What would you suggest? 
Currently using Seashore on the Mac, but I could also use GIMP. 
EDIT: Sample comic enclosed by request. Note that the paper in the word balloons and captions has a colour and texture that I'd like to preserve. 

A:

With Gimp comes a plugin Resynthesize together with a Python script Heal Selection. On Linux the plugin is contained in the package gimp-plugin-registry.
After selecting an area with the select tool:

We can "heal" this selection from "Filters > Enhance > Heal selection...". Here I made a random healing with 10 pixels from the surrounding:

A:

I would approach this in a similar way to horatio, but I would probably keep the original image in tact as much as possible (assuming you want to preserve it).
I'd create a similar texture to the paper like so:

It's just a noise texture against a subtle gradient with some distortions via a horizontal and vertical scale.
You'll notice some color variations that I applied using the Burn and Dodge tools to help it blend in to the existing artwork since the color is not uniform across the whole comic.
I used a Clipping Mask with very soft edges around the text removed to produce this result:

I used Photoshop to do this, but the same principles should apply in GIMP.

A:

Because you are editing out text (e.g. radically altering the original), one way to do this is to cheat:
Edit the image so that the yellowed paper is no longer yellowed. Blank out to your heart's content, then overlay a new all-over fake yellowing paper effect. This will be uniform.

