Don't believe everything you read on the Internet. ICMP redirects have to have the first 8 bytes of the original payload within them, good luck blind spoofing that much less getting the timing right.
Back in the days (~2001) there used to be this NZ guy on Undernet, going by the nickname Venomous.. he pulled a prank once by hijacking a shoutcast radio stream using ICMP redirection - he had to, because "his" box was not local to the stream server's subnet and thus, no ARP spoofing
Sure, what might have worked back then won't necessarily work today. But my point is, even if an ICMP redirect is supposed to contain 64 bits of the original datagram - whether that's going to be validated in any form or not, is entirely up to the receiving IP stack. No?
As for the sanity of networking stacks, past experience (teardrop, anyone?) shows that we shouldn't put too much trust into the various implementations, especially the closed source variants. I am arguing that, under normal operating conditions, a well designed network will have no legitimate use for ICMP redirect packets. So I'm just 1) advocating a "better safe than sorry" approach by filtering icmp redirects entirely and 2) suggesting that it doesn't (for a well designed network) matter too much that the fastforwarding path doesn't generate ICMP redirects.
As for the impact of ICMP source quench not being generated, the only time I've ever seen icmp source quench was back in exactly these days, when some freak hiding behind a fake shell provider with an OC-3 would hit our 128kbps frame relay with a multi-gigabit DDoS, knocking our entire ISP offline for a few hours. Needless to add that the entire flood of source quench messages the poor zyxel sdsl routers spat and choked out was -of course- totally pointless, if not absolutely counter-productive, as all the source addresses of the bad packets chocking our routers well were naturally spoofed. Oh well. Dude finally made it into the news when the FBI would shut them down for extortion.
I must admit though, that's a quite er.. historic file I linked there
Yet, there is a PDF which details some of the other issues regarding icmp redirection to be found at: www.cymru.com/gillsr/documents/icmp-redirects-are-bad.pdf