> As soon as everybody is paying spot prices

Which is never, because even then you are still paying some sort of taxes on top of the spot prices and also network fees.

The price of electricity from the network also has to include the price of delivery, while homemade electricity only has to recoup initial investment.

Of course this means given enough home installations (in places with enough sun) the price of electricity from the network will rise, more people will install their own stations, some will even disconnect, rinse and repeat. I read somewhere this exact situation is already playing out already in Pakistan.