All of my following comments are dependent on your riding style, whether or not you are aggressive around turns.
Yes, the 2010 through 2013 RTs rolled like pigs.
In my opinion, the RonBar gives you the biggest improvement per dollar spent. A massive and quite essential improvement. Those Spyders are nearly unrideable without the RonBar.
Next, you can try the spring spacers to stiffen up your suspension even more.
In my further opinion, spending big bucks on Elkas, or other suspension components is a waste of money for any further improvement. The only reason people spent money on the Elkas back then, was because Ron hadn't developed his bar until, I believe 2012, but I may be mistaken.
As others stated, the Spyder is designed as an on road snowmobile. those traits are inherent in the design.
If you have an opportunity, ride a 2014-2019 Spyder. BRP made some improvements to the suspension.
For the 2020+ model, BRP again made generational improvements to the suspension. There is always room for improvement, but the stock 2020+ suspensions are quite good.
Just my opinion, I could be wrong, and if I am, I'm sure someone on this forum point it out.