The thing is, there are Cisco & Juniper certifications that are far, far from entry level certifications. Especially with the CCIE and JNCIE, they’re people at the top of their industry, the exams are tough and the practical lab exams are just as difficult. People with those certifications are quite highly sought after (take a look for CCIE/JNCIE salaries).
I suspect when you talk about Cisco certifications you’re talking about the entry level CCENT and even the CCNA, they are common and they’re not that in-depth that they’d be providing you with all that unique of a skill set (or at all, really). At that position, they are just a nice to have - rather than a “this person has done these certifications”.
I work at a company with millions of £ on its networking budget a year, provides services for major UK companies, I have been able to go to various networking conferences, not just for Cisco, Juniper, but for others like Checkpoint (UG), and even non-networking companies like VMWare. I don’t think I’ve met anyone who could be deemed a professional at these places dismiss them as you have, and I’ve met people working at these huge companies with massive networks, talked with IBM engineers, HP engineers, Checkpoint engineers, even by companies in competition with Cisco and Juniper (like HP) they’re fairly well respected certifications as you climb up (from CCNP and up).
I’m not saying they’re absolutely necessary, but as you climb up as networker, especially if you’re not just an engineer, but someone involved in design and implementation you start to look like the odd one out if you don’t have these kind of certifications. They have a lot higher penetration than than the servers and infrastructure world.
The thing is, despite your scepticism regarding vendor specific certifications - and I’ve only gone through Cisco material - Cisco rarely ever present their proprietary solutions as the only option. They teach the standards, they mostly teach just pure networking - of course how to do it on a Cisco device, but they explain the theory, they explain it without the context of implementation too. That’s why they’re so common, because they’re also just useful vocational networking courses even if you’re not using Cisco equipment.