advice Do all 6N.com worth more than reg fee ? Should I be registering any 6N I find available ?

I think it is better to register without 0 and 4. And with double digits. The main buyers of digital domains are Chinese. They do not like the number 4 (death in Chinese) and 0.

But without the numbers 0 and 4, there are no free domains anymore. There are only free domains without the number 4. For example 570103 570106 ...

with double digits available 975508 982208 (23.11.2018)

866632 and 835550 - busy
975508 982208 983308 570103 570106 ... available for reg