XML is a good choice, that way the file can have a readable structure; why should the Nano provide CSV too?
Since you are graphing the output on a PC, just do a bit of preprocessing. A Perl one-liner could be the following:
perl -ne'/<(seq|val)>([^<]+)<\/\1>/ && print "$2".($1 eq "seq"?";":$/);' file001.xmlAntonio