However, if this home-brewed crypto involves coding (and requires users to learn an appropriate language), then it's possible that the entropy harvested from brains of such novices will be orders of (decimal) magnitude over the simple text scrambling.
For example, take simple DES implementation and customize S boxes and/or key generation phase. Do not publish the program except to your peers. Yes, S boxes filled with your dog's vaccination report are likely more sensitive to differential cryptanalysis - but how much ciphertext would that take, not to mention the analyst's time?
We are not talking here about someone specifically targeted. Custom obscurity works great when practiced massively, as de-obscuring has to be done manually in each case.
The bigger issue is whether privacy and secrecy should be simple so that anyone can use it. We may be well past that - standardized security is obviously dead in the water. If security is important and affects one's life, then one should invest effort in it as the one invests efforts in hygiene, education, car maintenance etc.
The requirement that security must be simple so that even idiots can use it is a diversion, a fallacy that imposes inherently weak crypto on all. This is the biggest lie plaguing crypto since the first crypto war.