I've had lots of bikes, including a GL1100, GL1500, and GL1800. I bought the 2004 GL1800 new in 2004, kept it 80 months and logged 78,000 miles. It was a great motorcycle.
Consumer Reports is very negative about the Can-Am Spyder reliability, and so am I. Search DESS and LIMP HOME on this forum. I could do without some of the electronic complexity.
Maintenance on the GL1800 is also easier and less expensive. The rear tire can be removed in 10 minutes. The oil and filter were very easy, whereas the right mirror and a couple of side panels must be removed to change the filter on the Spyder, plus you initially need a Torx and Allen wrench to drain the oil. Lots of us replace the drain plugs with more normal plugs.
Communication on the GL1800 was pretty easy - a couple of speakers in each helmet and plug in the wire. I think we had 6 easy-to-see illuminated presets plus the weather bands. I'm not sure about the Spyder but I think some folks use a 'dongle' and others upgrade the speakers. My radio is so unintelligible that I don't even fool with it.
The transition from 2 wheels to 3 appears pretty easy since you don't tip over, but a trike/sidecar class will help a whole lot.
My comfort level on the Spyder goes up to about 65-70 indicated, and the belt vibration commences at 71 to 73 so I back off there. On the GL1800 80 mph was very comfortable, and on the FJR1300 85-90 was like being on rails.
I ride the Spyder and am delighted to do so because of low speed stability and comfort. I don't worry about tipping over at gasoline stations, at low speed hairpin curves and turning into my gravel drive. I've ridden 5000+ local miles in 7 months. I started a 400+ mile day last month and got the LIMP HOME screen about 98 miles from home. I hope to make that trip tomorrow.
These comments looks pretty negative, but I think they are realistic. I am so glad to have this machine and to still be able to enjoy the wind in my face. Good luck with whatever you decide.
BTW the CMA/IBA rider in a comment above is doing the Jacksonville, FL to San Diego, CA IBA ride in 50 hours later this month. I am so interested in watching that ride as it proceeds.
-Bill