Andrew,
Upon reflection, I think that GoodReader meets my needs with minimal inconvenience. I can browse to a link, download the file, and then immediately export to Gaia. I'm not sure that adding a browser to Gaia would be the best use of limited resources (i.e., I'm not sure I would vote for it if it were suggested).
Regarding photos, thanks for the information on the limitations of GPX files. Some of the tracks I use are in KML format, which be imported into Google Earth with photos. I believe that Gaia now supports importing of KML. Would those photos be included when KML/KMZ files are imported to Gaia?
I have been using Gaia for about four years now, and I think it is a wonderful product. However, I mostly use it to guide me when I hike, using a track that someone else has recorded. I.e., I rarely record my own hikes, but would use the photos to keep me oriented, help me identify landmarks along the way, etc. So I would not be particularly interested in adding photos the hike.
Thanks for all your help, and for your excellent app!
Doug