Visible should provide the PayPal discount to existing customers. I recently switched to the $30 plan since I was having some issues with the old $25 one. Generally, I'm pleased with the service, but Visible is much more appealing at $25 a month. $30 is closer to some of the offerings from carriers with better support like US Mobile, or even direct Verizon if you join a group on CircledIn or something.
It feels like this "new customers only" policy is a slap in the face to existing customers. The funny thing is that I could port out to a different carrier and port back in as a "new" customer and get the discount. This would be a lot of hassle for me and would cost Visible to ship out a new SIM card. With this in mind, it really makes no sense for them not to offer it upon request.
I'd like to stay with Visible a lot longer, but with policies like this it feels like they just don't care about retaining existing customers.