I went from a Boulevard c50 to the Voyager 1700.
The Voyager is instantly more comfortable on the open road (obviously). You really won't feel the bumps that used to send shockwaves through my spine on the c50.
Storage is great, cruise etc is great - and a long as you don't get buffeting, the wind protection is fantastic. I solved my buffeting with a larger shield than stock. I have to look through it though... any lower and I get helmet buffeting.
The m50 will be a lot more nimble. You'll scrape around corners on the voyager.
Also the off-the-line power of your m50 will be a lot better. I know it seems counter intuitive but the big 1700 is sluggish in comparison to the light, sportier c50/m50 bikes.
Fuel range will be only slightly better on the Voyager (230km on the c50 vs around 250-280km on the Voyager before you'll need to fill up).
You may experience trans whine on the Voyager.. take a test ride, see what you think.
It's a good step up IMHO. My partner falls asleep on the back. She woke up as I was going around a corner once, she looked at the road and it startled her awake with a jerk. Scared the **** out me mid way into a turn
Just goes to show how comfortable the rear seat is on the voyager though!