Considered yes, but decided against it. ROM is very stable & battery friendly anyway ATM, no reason to change anything if you ask me...
I always go through stock GB myself
If you want a new bootanimation just search for it and look for hdpi one. When you've downloaded it make sure it is named bootanimation.zip and use any root explorer to replace the mackay one in /system/media.
First animation (orange android) is kernel animation. Recovery is also part of the kernel partition on i9000. So if you prefer CWM (I honestly don't get it why) you can flash any other ICS kernel with CWM recovery, just like @limnaln already wrote you. That way you will get rid of TWRP- and also of the kernel animation. BTW, no other ICS kernel is as fast as stock kernel of this ROM. Among other custom kernels the fastest one is Semaphore 1.3.0 and it has about 90% slower performance. It has Semaphore CWM recovery.