Sorry to hear about the fuel strip issue. Lots of those have occurred.
The big advantage to the BMW OEM saddle bags and top case is that one key fits the ignition and all the bags on your motorcycle. Bags/Top case fit & finish and mounts are excellent. The big dis-advantage is that they are also expensive.
If you ride a lot on curvy roads and prefer carving canyons, the weight is lower down with the saddle bags. The top case raises the center of gravity up higher. If you're solely concerned about handling, the lower center of gravity is better.
Therefore, a HEAVILY loaded top case will negatively affect handling. An empty top case should have hardly any effect at all. I weighed my 32L pannier cases; they're about 12 pounds each, although the left one with the stainless steel exhaust heat shield is a few ounces heavier. The empty 28L top case alone is lighter, (unverified post 10 pounds?) but this is NOT taking into account the extra mounting hardware. Taking all this off the bike just to weigh it would be a PITA.
Little help please from you guys with a top case, scales, and wrenches, and absolutely nothing to do.
A top case can induce a high speed wobble, particularly if riding fast solo. I witnessed this recently. Passenger's body filling the gap reduces the tendancy, I am told. If you drive <55, you need not worry. It's a high speed issue.
It is easier to filter traffic with only the top case attached, as the pannier cases stick out on the sides. BMW designed the sidecases to be only slightly less width than the bar ends, levers and mirror tips. Look at fleuger99
New VStream Z2443 Installed Yesterday post. It's very close on both sides, but it WILL clear.
http://www.advrider.com/forums/showthread.php?t=781223 Rider skill, confidence, and fear of lawsuits/citations will vary.
If you are lane sharing/lane splitting so slowly that your bike is weaving and teeter-toddling, the side cases can hit the vehicle beside you. I speak from experience. When you're moving fast enough to travel in a straight line, if the bar ends clear, you're generally OK. As traffic jams flow, then suddenly stop, the transition here is awkard and unpredictable. When leaned over, I have skuffed the TOP of my pannier case, not the side, on lane divider posts in a curve, so this should be considered. IMO Panniers alone look OK. Panniers with top case looks complete. Top case only without panniers is practical, but ugly ! Fugly?
http://advrider.com/forums/showthread.php?t=363361
Panniers will help keep the bike off your legs, and your passenger's legs, in a tip over. In effect, rear crash bars. Reduce damage to expensive final drive housing and turn signals. Could be easier to get away from the bike in event of a slide/crash.
The 28Ltop case requires the large rear luggage mounts, luggage rack, luggage grid, and a different plastic trim piece.
http://www.realoem.com/bmw/showparts.do?model=0490&mospid=53242&btnr=77_0152&hg=77&fg=42
Optional scuff guard and passenger back rest cushion are offered. All add cost and weight. To it's credit, it fits a lot of gear or a full-sized helmet. It's easy to access. Lane splitting feels easier and is less stressful. Passenger feels more comfortable with the backrest. A additional $180 BMW 50L softbag or waterproof 45L Ortlieb bag is less likely to be lost off the back. Reflector strips and LEDs can be mounted higher. It's always nice to have another LOCKING waterproof case when camping, or leaving the bike on foot. Downside? $800 total cost? Top case may block your rear escape off the bike if/when you crash/slide. Top case can't protect your legs, or final drive housing in a tip over.
Finally, although NOT TESTED, if the low fuel warning light is ON, both tires fully inflated, and panniers and top case are all 3 attached and locked, the motorcycle should sink more slowly when driven off a bridge into the bay.
Verification volunteers requested.
GIVI and other case makers have unique features like built-in reflectors, aluminum construction, a light inside the top case which comes on/goes off automatically, and various sizes. Do you want a mirror inside the lid? More running lights for safety? Surely there is a case system to suit your riding style and budget.