Pre-emptive hard drive replacement?

I replaced the original hard drives in our 2 S3 OLED TiVo's (December 2006 and January 2007) in September 2008 with 2 Western Digital AV-GP WD10EVCS drives so they are about 5 1/2 years old now. I've been tempted to pre-emptively replace them with 2GB drives to try and head off possible failure with loss of shows (and with the side benefit of gaining more space). We've had good experience with hard drives in computers and TiVos. Our original S1 drives were still working after 6 1/2 years and 9 years respectively for example.



I was curious if anyone else had thought about replacing their drives as they started to get older to avoid a failure.



Scott