Very cool, thanks for sharing.
Presumably one could set up a cronjob from another system to do such maintenance, even.
(Might consider djmount for upnp file manipulation too, for that matter.)
And if you are able to set up a user / certificate, should be able to do so passwordless.
Seem like you should be able to scp directly into your dropbox folder, and avoid ftp entirely.
For 1., you might consider find /mnt/mmc/ -name "*.log" -delete
For 2., you might consider sshfs
[Never mind the scp comment, just noticed you tried it. Oops.]