Is there a way to increase thumbnail size?
The absolutely easiest way is to use Microsofts Powertoy “Resize pictures”
No, I don’t think you’d want to do that… The Live is going to scale the thumbnail to fit. Increasing its resolution is not going to do anything visible on the screen.
Now, if you’re asking “how do I make the thumbnails BIGGER on the screen,” the short answer is: You can’t.
The resolution is 120x180, any other resolution will be upscaled/downscaled by the WDTV so you are better to use the real resolution.
I know 200x300.
The Live caches them in 160*240, give or take a pixel, so no reason to make them bigger.