Maybe one of the interesting "things to do" would be to write a small daemon
that captures those UDP packets to 255.255.255.255 port 5678 (MNDP) and
stores the latest one received from each source. It would have to have access
to the outer IPIP header to do that.
Then, it could regularly dump the collected "latest packets" in a tabulated
text
file with the fields that there are in these packets each in a column. When you
look in wireshark (which knows about this format) you see it is quite easy to do.
This table would present an overview of the MikroTik routers in use, and could
help identify possible problems with the tunneling they do.
You could also stop handling them as an error condition.
How would such a daemon have to be written so it can run at the gateway?
Could it just do a pcap with the appropriate filter?
Rob