I've had a 650gs dakar for some years and it's worked for me for everything I've done. Taken it long haul many times, including interstate, and on plenty of dirt riding. Granted it has more suspension and a better seat than the regular 650gs. It doesn not require premium, 87 is fine. Gas mileage has been excellent, often in the mid 60s.
I'd say it's a more versatile bike than the wee, and lighter too. One thing to pay attention to is the fueling. The early ones (up to 2002, but i may be wrong) had surging problems.
Another plus is the f650.com website, a wealth of info about anything you'd need to know if you own this bike. Good luck.
2004 Moto Guzzi V11 Cafe Sport
2003 BMW F650GS Dakar