Hmmm. I'll bite. I've had a few middle weight bikes that did both cty and touring work (my vice is BMW but there are plenty of good optons about).
The pick of the current Japanese middlewight bunch seem to be: Honda CB400 (4 cyl); Kawasaki ER 6N; Suzuki Balius (650 Vtwin), Suzuki DL 650 VStrom (if you're tall - seat hieght is 820mm) ... these seem to be around the $10K mark and a few have ABS available. Some have good luggage options. More power and generally better brakes than a scooter ...
I'd have to say, these aren't scooters and you have to realise you're changing your riding from scootering to biking. Sounds trite, but what you get on a scooter - light and zippy, twist and go, upright posture - isn't easily found on a bike. I ran my BMW F650CS (fuel-injected 652cc single, 37Kw / 60Nm; 193Kg wet) as a citybike / scooter alternative for years (also as a light tourer, doing 3500km in a week a few times) and I thought I was effectively scootering, if slightly faster and with better suspension, luggage and brakes (ABS). I was wrong! Even the wee FLY 125 is quicker than the 650 around town because it's so light and so easy. City riding is rarely about power - though it is sometimes about brakes and horn! Scootering is just so easy, I wish I'd come to it a decade ago (back then I couldn't adjust quickly from large road bike to small scoot - all the test rides I did just made me nervous on both).
Seems to me the bike you'd choose is one to complement your scoot (unless you consciously want a different experience, like a crotch rocket) - so an upright posture, neutral steering ("quick" bike steering isn't at all like quick scoot steering, IMHO), supple suspension, flexible torque spread - these 'd all be more important that outright power. So I'd be looking at naked bike capable of the bit a scoot ain't so good at - eating up country miles. I'd include the Triumph Bonneville in that group, even though it's pricey for the performance you get (two other interesting bikes in that retro style are Guzzi V7 (750cc, shaft drive) and Ducati GT1000). Other surprises if you're going for complementarity would include the "huge" naked bikes from Suzuki & Yamaha - incredible value and the power is still controllable. The big BMWs are there, but they're a lot more expensive. BWM do now make factory lowered bikes in their roadster range - F650GS, F800R, R1200R - so they're a little less intimidating for te vertically challenged (i.e. me!). My R1200R + wee scoot is a great combination .. even if I find the big one's steering a bit slow at first, after the scoot.
If I were buying on a budget, could cope with the seat height and could stand a chain, the Suzuki DL650A VStrom with ABS and luggage at $11K ride away would be very hard to go past. A true all rounder - a much nicer bike than its 1000cc sibling - and will run with anything, all day, on any road, unless you're doing silly speeds. (If you have a Vespa, then I guess it's retro Bonnie @$16K, V7 @$15K ... or nothing).
My 2 cents from 30 years road riding, after learning on an Auto Union 70cc rope-start step-thru ... YMMV.
[ps .. to me, the GS500 and similar are a waste of money - cheap enough, but lack power, have decades-old handling (no rigidity in their chassis), poor brakes, soggy suspension. They are quite a few bike generations behind current standards. For the money, I'd get a large scooter and have more fun. A GS500 does make sense if you think of it as buying an old bike with all-new parts ... I guess.]