I guess IP certs won't really be used for anything important, but isn't there a bigger risk due to BGP hijacking?

No additional risk IMHO. If you can hijack my service IPs, you can establish control over the IPs or the domain names that point to them. (If you can hijack my DNS IPs, you can often do much more... even with DNSSEC, you can keep serving the records that lead to IPs you hijacked)