Both suggestions are correct.

Texturing is an art in itself and requires a little bit of black magic to be able to use correctly down scaled texture images to tile correctly and maintain resolution.

TBH, I have done the same by working in photoshop at as high a resolution as possible then once complete to speed up texture loading and render times I have resized the image file to a more manageable size. This should keep the details, but never overwrite the high res one as you will always be able to manipulate changes at the high res and overwrite the one used for rendering...

Also I would use the PSD file plugin in the hypershade as you can get more control over the different layers you can create.