Hi Peeps, interesting topic.
As a retailer, I notice when people upgrade and why.
I reckon there is a large percentage of new kites are sold to those who are keen to have the latest gear each year. They can usually afford it and are happy to shell out the bucks for keeping their gear up to date. Usually, the kites do not show signs of wear and tear in only one season so they avoid the hassle of repairs, replacement parts and upkeep. They also keep up with the latest performance and safety with bar developements.
The Buy and keep guys. These guys tend to be married with kids, have mortgages and are more fussy about what they buy. They buy every couple of years and ride and love their gear as it is carefully chosen and fits their requirements. In reality, their requirements don't usually change and so their kites keep filling their needs so there is no need to change. Eventually the kites are so well used they start falling apart and needing maintenance so they start demoing. Like I said, they don't hurry their decision and choose wisely.
The thrifty and clever buyers are the ones who buy off the new upgrade guys. They get one season old kites in good condition and allow a full season to see what was a hit and what was sh1t by allowing others to trial and test properly for a full year. They buy each year at reduced prices and sell them on for not much less each year.
Most "A" brands kites do not need to be upgraded every year. The quality of cloth in good brands will see the kites work well for a full year to two years then degredation in the cloth starts to effect performance and durability.
"B" brands should be replaced every year as the cheaper cloth breaks down quickly and performance starts being effected about half way through the season, and they are blown out by a full season.
At the end of the day, if you can afford to replace your bread and butter kite each year, you can, but maybe not essential, if you can't afford it, just keep it until just when it starts becoming unreliable, then move it on.
Nothing, and I mean NOTHING comes close to the look, sound and feel of a crispy, crackly new kite being unrolled for the first time, and the smile when you launch your new pride and joy. Oh yeah!
Read less hype, do more research, talk to real people on the beach that own kites and fly them and make careful decisions and you'll never fly a bad kite

DM