Primes are useful because multiplication is computationaly easy. Factorization is not. Are you suggesting 30 mod prime makes factorization easy?
Yep, you divide by 30 and the remainder tells you what spiral it is on
so now you only have to check 1/30th of the field
I don't think this really matters. You would still need to use a very large amount of computing power to figure out the private key from the public address, more computing power then would likely ever be available in any of our lifetimes.