Assuming one isn't a noobie or decided upon entering a new area of fly fishing (say starting out on saltwater), I think the new rod "thing" may be very dependent on the type of fishing one does. Steelheading, salmon fishing, saltwater and other areas where covering the most water is important lend themselves to newer, "better" rods that are lighter, faster and can throw line farther. In these cases, one can see the benefit of the newest "advances" in rods.

On the other hand, if one (like me) spends 99% of one's time creeping around small creeks for trout and blue-gill - the newest and best doesn't add much. I'd guess 100% of the fish I catch are within 40' of my position and I can easily cast that far (with reasonable accuracy) with a 7 year old 4-wt Orvis Power Matrix or a 10-year old 5-wt LL. Bean First Cast that I bought for my son when he was 9.

My wife bought me a 5 wt Zero Gravity about 5 years ago, I've used it a few times out west, that's about it.