I am trying to understand if creating VPNs have negative impact on the Solace infrastructure. What should I be worried in a Shared Solace environment w.r.t VPN's
I've never seen any noticeable negative impact from creating Message-VPNs. I have seen CI pipelines that create a VPN, run a test suite, then remove the VPN.
The only exception to this I would say is if you are creating and deleting at a high rate (many a second) - then you might start stressing the management interface.
VPNs were created to allow for separation of message naming space and broker configurations for multi-tenancy. In general, I'd say use them more rather than less! Especially in a shared environment. Please remember, though, that just because a section of your messaging activity is in a separate VPN doesn't mean you shouldn't plan and monitoring your messaging capacity at the system level.