I think it makes sense to have a fresh new poll quest for every year. The reasons are:
keeps each year's thread a reasonable length
it's ok to repeat some polls after a few years, since opinions (and monks) change over the years, and it's interesting to see that too for some poll questions
it's really not that much trouble for a prospective poller to click two or three links to review past year's poll questions before posting their poll suggestion
using the "2007" poll idea quest thread makes no sense since it's 2008. It also makes Perlmonks look out of date to newcomers (either when they go to submit a new poll suggestion, or when they see a new post on it pop up in Recent Threads).
It's not sustainable to keep just one poll ideas quest thread going and going.