The GPSAltitude progam referred to, I can't seem to get working.
The other option, of opening the file in Excel,
I think, from the other thread, you now have GPSAltitude working OK
It is simple enough to get the altitude into a spreadsheet but I don't think it is a simple matter to get accurate altitude data from it, as can be seen in other threads.
Using gpsbabel for converting routes into a .csv file there is a couple of options.
Using .xcsv - this requires a style file to tell gpsbabel what to process, I simply edited an example file from the gpsbabel documentation. and set it up for lat, long and altitude ( I have to do this to import into my OS mapping)
Using .unicsv - It tries to create a column for any data it sees in the file to be converted, so for a
standard .gpx it has columns for line No. lat. long, altitude, and time. Then paste the file into an Open Office spreadsheet using the comma separator paste option which puts the data into columns.