I started on Yamahas and was loyal until I rode a 2011 XP that just 'fit' me and my riding style. I've never looked back.
About a week ago I borrowed a stock '09 XP from a friend to go riding with my wife to get out of the house for a few hours to avoid the mountain Janurary Blues. We bumped into a group of Factory Skidoo riders (Skidoo has a test facility here in Grand Lake) who were testing prototype sleds (a 2017 model among them!, sorry no pics). My wife and I know most of the test riders and managed to talk our way into a test ride of a 2014 for a couple of minutes. This gave me a chance to ride the different sled generations (09 XP, '11 XP, '14 XM) back-to-back-to-back.
The '09 felt like a 'TANK' compared to the '11. I'm not a big guy (140#, 5'9") and I have a hard time getting the 09 on one ski and keeping it there. The '11 turns easily, has better/crisper throttle response (Etec 800), and is just plain easier to ride... That being said, the '11 felt like a 'TANK' compared to the '14! I was amazed at how easily, even compared to the '11, that the '14 would turn and manuver. I could simply lean on one foot or the other and the sled would carve a turn in that direction. To say the least, I was impressed.
I guess this is a long-winded way of saying, at least for me, upgrading to the newer technology/new sleds makes sense if you can afford it. I like to tinker and buy parts for my sled as much as anyone, but you just can't beat what the latest generation sleds can do. Yes, any handy rider with good tools, a nice shop, and (most importantly) the free time can upgrade their current ride to keep up with this newest generation of sleds. But in my opinion, between the time and the money you'll spend trying, it's not worth it. You may be able put together a sled to keep up with the new sleds, but it probably will not be as reliable, might end-up costing you MORE money, and certainly will not have a warranty like a new sled (usually 3 years if you Snow Check).
To each their own. There will always be guys/gals that are satisfied with their current sled and level of skill it takes to ride it. And then there are people who always want to push the envelope of their sled, available technology, and their ability to ride it. 'Life is the sum of all your decisions', but there's no 'right' of 'wrong' choice here. I'm just glad we have so much to choose from!