I own a 2018 RTL, and it is the only Spyder that I have owned, so I can't make a comparison. Here's what I have to say. The Spyder has it's small idiosyncrasies, which are surmountable. Mine just spent a month in the shop with 1960 miles at 3 months of ownership getting the problems ironed out. Many more have absolutely no problems, but my case illustrated one glaring issue with Can Am, and it's not the machine!
Service is the main ingredient of a happy customer. Absolutely do not buy a Spyder from a dealer that doesn't have an outstanding service rating. If there are any negative reviews about service, skip that dealer and go farther down the road. Believe this.
There is much made of the dash in the new models. I can't speak to the earlier models, but this dash does what it needs to do. I can see the speed, RPM's and other information clearly in any sunlight. If you have the 20.8 (or later) firmware update it functions correctly, show average MPG, miles to empty, etc. I has some growing pains with the apps, but I don't use that stuff anyway, so I can't comment on that.
The 2018 RTL is a heavy bike. Unnoticed by me until I did a 2 up ride with a slightly heavy passenger, the 2018 RTL wallows in corners. Riding solo I didn't notice this. A front BajaRon sway bar is a must. I ahven't got one installed yet, but it is very next on the list. Check out my accessories, a lot of them are to improve handling and ride.
I run mine at around 70 mph, averaging around 32-33 mpg. They say it'll get better, but I really don't care. It's a 1000+ machine. At 60 mph I get around 38-39 mpg.
Other folks have said the 2017 has better build quality, and like the dash better. Some folks have made mention of reflective stickers replacing real reflectors on the newer bikes, but my 2018 still has all the reflectors as far as I can tell.