Will changing just the front tires to car tires make a difference in the rolling sensation?
It'll make
some difference/improvement to that '
rolling sensation', Bob; but not as much difference to that as a sway-bar or coil spring upgrade. :lecturef_smilie:
However, upgrading to good quality car tires and running them at an appropriate (lower) pressure for the (lighter) load of a Spyder vs that of a car will make more of an improvement to the ride and handling, especially if you ride even just a little harder than sedate cruising.
It's one of those '
horses for courses' things... A Sway Bar Upgrade will reduce the rolling and keep the bike more stable thru turns; but then the OEM tires will be the limiting factor on your ride & handling.

While upgrading the tires & running them at the right pressure will improve your ride & handling, but it will leave the OEM anti-sway noodle thingy as the limiting factor on keeping that rolling under control and holding the bike level during cornering! :shocked:
Mind you, even tho it'll undoubtedly reduce the 'straight line rolling' that bothers many, one '
other' thing that many may overlook when upgrading the sway bar, is that if you
do happen to push further towards the cornering and handling limits of the bike, running a sway bar that keeps the bike more level during cornering means that you as a rider (&/or the pillion also!) will need to increase your effort to counter the forces that'll feel like they're trying to throw you off the outside of bike as you corner harder cos now it's easier to do that!! Similarly, if you upgrade the tires & get the improved grip that comes with it, especially when running them at a more appropriate pressure for the load, you'll probably find you've increased the need/desire for that sway bar upgrade while cornering, cos the ramped up cornering forces will also ramp up the body roll & the on feeling that the bike is trying to throw you off towards the outside of the corner when you take advantage of that extra grip & better 'turn in'!! :yikes:
So... which do you want to do - first??
You do know that it's infectious, don't you?? :dontknow:
Add or upgrade
just one thing like either of these two, things that'll make a noticeable difference to your ride, and you'll soon be finding excuses to justify adding more farkles &/or upgrading something else! :roflblack: All good tho, we all do it!

So you might as well just succumb to the inevitable, and
upgrade both the sway bar AND the tires, all three of them! 
hyea:
Go On - DO IT!! You know you want to.
:lecturef_smilie:
And if people are being truly honest with themselves, very few ever regret making any of these particular upgrades! :yes: