There is nothing in common between the two machines, in my opinion, beside the fact your knees are "in the wind" on both.
So do NOT set yourself up for any disappointments by making any direct comparisons between the two machines. As was mentioned; keep your expectations to a minimum and let the Spyder be what it is. Many have found it to grow on them, to where they are much happier with it over their previous trikes.
- Handling: You should like the Spyder better. It is more stable, being a reverse-trike. Less likely to tip-over. However, some find the Spyder to be more "jerky" at first -- which takes some getting used to, as well as learning how to handle it.
- Steering: Should be somewhat similar, since counter-steering on a trike doesn't work. You may find it easier to steer after a few hundred miles.
- Riding Comfort: That is a personal thing. Some like their Goldwing better, others do not. The Spyder is likely to ride a bit stiffer than your trike, but that is adjustable.
- Engine Power: The Spyder is NOT the Goldwing's power-plant. The two engines are entirely different from each other, and should be operated as such. Low-end torque on your GW will not be there with the Spyder. However, once you learn the shifting technique and running at higher RPM's with the Spyder you should get used to the difference between the machines.
- Shifting: This is probably one of the areas where big-twin and Goldwingers have the most trouble getting used to. Just remember, the Spyder runs at higher RPM's, and will not have the low-end torque you may be used to. Most Winger's and large v-twin riders are used to running RPM's between the mid-2,000 and 3,000's. You won't be doing that with the Spyder if you want it to provide its type of performance.
- Maintenance: You probably had to do less maintenance on your Goldwing, since they are practically bullet-proof. However, maintaining a Spyder isn't too bad... it is just that you have to do it. In addition, the Spyder is relatively new to the market, and has had its "quirks" to deal with. Where the GW's technology has been around for a long time.
- Sport-vehicle versus a truck: Consider the Spyder to lean more toward a sports-vehicle versus a big-trike being a more "lumbering" vehicle. When you get used to the difference and handle it accordingly, you should like it.
- Camaraderie: You will not lack for camaraderie among Spyder owners. Spyder owners, generally, are a tight-knit group that like to get together and socialize, and welcome new people to the fold as they arrive (as you will learn from Spyderlovers.com).
I currently still own (and ride) a Harley Ultra-Classic (for as long as I can); and also own a RTS-SE5 (with trailer). I like both machines for what they are... but recognize they are different. I feel safer on the Spyder, and my wife prefers it now.
Overall, I am very happy with my Spyder purchase, and believe you should be also. However, make sure you take several test rides before you buy (one ride is not enough).
Good luck to you!