I doubt anything would keep you warmer than the snowmobile gear, either. If you switch, it won't necessarily be for warmth, and it won't be for convenience either, since it still takes forever to dress for a winter ride. It is strictly a matter of bulk.
I have some heated gear, but I seldom use it. Too hot, IMO, even with a good thermostat, set on low. My wife loves it! Sound familiar? "Honey, turn up the thermostat." Biggest problem, especially with two people using heated gear, will be that the electrical system is limited in capacity. Also remember that the Spyder only charges half its rated amps at 4,000 rpm. If you use heated gear, keep the rpm up. You can likely get by with just two vests, and maybe even with two jackets. Nancy has used both jacket and gloves on her RS, and they have a lower electrical system output. If you add gloves, pants, or socks, you may have to juggle things on and off. Leaving the foglights and heated grips off, are about the only options, although the audio system might help, too. Without an ammeter, it will be hard to tell when you are over the edge. A voltmeter might not tell you until it is too late. You'll have to experiment a bit.