I dont know why youre wasting any more time and money on it other then sending it to a professional recovery service.
On the first page you mentioned you already booted from a Diskwarrior disk and it did not see the drive, which means there was like a 99% chance the drive was simply dead. If a Mac OS disc, Mac OS itself, DW and Data Rescue cant even see it, the drive is gone and putting it into another enclosure is not going to magically bring it back to life. Its time to either give up or send it to a professional if the data was really that important.
If the drive became 'frozen' and wont spin up, which Seagates seem to have a tendency to do, you can do what I did to one of mine a couple weeks ago and shake it around and see if you can loosen it up, but other than that, its a lost cause. Mine crashed after my G5 kernel paniced and overheated. I got lucky and shaking the crap out of it loosened it back up and so far its still running. Youll know if this is your issue if you can hear the drive 'chirping' or making a beeping sound when its trying to spin up.