Please consider yourself a NEW RIDER if you haven’t ridden in 25 years. The motorcycle accident statistics show that a lot of accidents happened to middle-aged RETURNING riders. Riding is a perishable skill. Take riding lessons, and take it very easy until you have regained your skills.
I own both a SV650 and a GS500 so here are my thoughts regarding your concerns:
SV650 –
Seat is about 1.5″ higher than the GS500, so this bike feels taller and bigger to me (at 6’0″). The bigger size and the extra power made it harder to ride until I got more experienced. Fuel injection and liquid cooling are great. If you’re concerned about the sport riding position being uncomfortable, get the naked version (more upright) instead of the faired version (more leaned forward). I haven’t heard that it’s more expensive to maintain or less reliable than the GS500.
GS500 –
The lower seat felt comforting for me as a new rider, but now feels a little low. Overall the bike feels more petite than the SV. I’m guessing the higher handlebar position compared to the faired SV w/ lower clip-ons made you feel the GS had a higher CG. The carburetor is a little cold blooded and requires longer warm up. Mine GS is running rough when cold and at low throttle opening (seems too lean, a common complaint) and I’m having a shop adjusting the carburetor (shim the needle, adjust air-fuel mixture screw) for $160; hopefully this would improve it’s rideability when cold. Less powerful and less polished than the SV (newer design), but extremely new rider friendly. Still very fun to ride and capable after you gained experience (I’m keeping mine because I still enjoy it), but some people wish for newer/bigger bikes after some time. Valve inspection/adjustment interval is 4k miles, so unless you’re the home mechanic type, this is an added expense to consider.
Used bikes make a lot more sense for new riders.