When I see a layout for something I like that has thin traces, I make the image greyscale, then use a "soften" filter to smudge it. That spreads the traces out a bit, so I then use a "highlight/midtone/shadow" filter to darken those greys that have been added on the perimeter of all traces and pads. A few runthroughs until its thick enough, then I flip back to a black and white image to clean up the excess. At that point, there may be a few places where the expansion of pads has made thigs perilously close and at risk for solder bridges. So I digitally remove some black from the image with a paintbrush or other tool, just to make some space.
Keep in mind as well that with application of heat, some photopaper will occasionally "splat out" so that traces become fatter than they originally were.
And yes, groundplanes can be a royal PITA if too big. I always try to have a ground-surround on boardsm, but if any segment of it covers too much surface area, it serves as a heat sink when soldering, and makes for lumpy clumpy solder joints. So I may try and reduce some of that surface area, whether digitally, or with an X-acto blade after transfer (but before etch), just to avoid the problem.
