Just to clarify - when you say you are going to a routed connection i assume you mean on the outside interfaces of the routers ? I'm assuming this because you mention HSRP running between the firewall facing interfaces on the routers. So in effect the internal interfaces of the routers and the outside interfaces of the firewalls share a common vlan/subnet.
If the above assumption is correct then a further assumption is that the new switches are interconnected via a L2 link, either a trunk or more likely an access port config with the ports in the shared vlan.
If all the above is true then the standard setup is to connect firewall1 to switch1 and firewall2 to switch2. This will not introduce a single point of failure because -
1) if switch1 dies then firewall1 (active) will failover to firewall2 and firewall2 has a path via switch2 to the routers.
2) if switchport that connects to firewall1 dies then firewall1 should failover to firewall2
3) if firewall1 dies then firewall2 becomes active
4) if outside interface on firewall1 dies then again firewall2 becomes active
note that 1, 2 & 4 assume you are monitoring the outside interface on your firewalls for failure.
Edit - obviously the default-route on the ASA firewalls will point to the HSRP VIP on the routers. And the routers should use the VIP for the outside interface on the ASAs
Edit2 - sorry, been away from CSC a while so i'm getting a bit rusty Obviously the internal interfaces of the routers will also be routed connections which is fine. What i said still stands ie. they are running HSRP between themselves and they share a common vlan with the outside interfaces of the firewalls.
Jon
