I don't see a lot of difference - for good or for bad.
Is it 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16? I guess that would cover 99% of local networks.
I wasn't aware virtualbox has firewalling at the virtual NIC level - my 4.1 doesn't; It's either host-only, bridged, or nat - of which bridged is unlimited, host-only is useless, and nat cannot (as far as I can tell) be firewalled at the virtual NIC level. So how do you do it?
A VM can be put on its own VLAN with a traffic routed through a secure firewall. I don't think Arc is as doomed to be insecure as many are claiming.
It isn't doomed to be insecure, but its security, portability and convenience/usability have a nontrivial tradeoff which is ignored by the original description. If it's portable and convenient, it is likely going to be lacking on the security front.
The original Cisco firmware for the E3000 also has vulnerabilities, which were never fixed.
I try to keep my network secure, but e.g. Cisco/Linksys E3000 hasn't received a firmware update in a long time, and it has known exploitable bugs - right now, the fact that it is only accessible from inside the NAT, and that webpages can't do arbitrary accesses is what keeps all those E3000s from being exploited.
(My E3000 has been running dd-wrt, so it's not vulnerable to those problems; but I had to manually upgrade the dropbear ssh because of vulnerabilities - latest official dd-wrt for it is still vulnerable)