The advantage of wccp is that you can intercept just the traffic that you need and let the rest go through normally.
A disadvantage of a L4 switch is that it might not be able to handle all the not-interesting traffic.
[multicast traffic, high volume,...]
The advantage of a L4 switch is that you can even see the URL, and decide if the requested content is cachable or not and so just redirect the necessary traffic to the cache.
To overcome the problem of L4 switch not able to pass all traffic, you can use policy routing on your core router and redirect the HTTP/FTP,... traffic to the L4 switch and route the rest.
Regards,
Gilles.
