PARTS ADDED...
Power Commander. More power, thank you very much. And so far, it has endured a lot of rough roads. One nay-sayer suggested the electrics inside the little magic box may fail due to constant vibration from riding in the dirt, but so far so good. I have encased it in a bit of foam to cushion it.
Radiator Protector (Metal Mule). Essential out here, and the MM guard is perfectly adequate and half the price of others.
Rectifier Protector (Touratech). It came with the bike, but seems like a good idea - I'd say all forward facing protection is essential for prolonged riding on dirt and gravel.
Roll Bar (Touratech, upper part only). When I first saw them, I thought they might only provide limited protection. After numerous drops, I'm happy that they are all I need. The geometry of the Tenere means that the Barkbusters take most of the fall on flattish ground (and of course panniers help further in holding the bike off the ground). The plastic crash panels on the fuel tank do a good job at soaking up the shock, and the TT roll bars protect the lower front end of the bike when it's dropped on uneven ground. I think the big crash bars such as the SW Motech ones are over-kill.
Bark Busters + Storm Wind Deflectors + Bar-end weights. ESSENTIAL. I've dropped the bike so many times now, and only recently managed to slightly bend one of the Barkbusters when I came off heavily on a nasty decent. Nearly every time the bike goes down, the Barkbusters take the brunt. The Storm wind deflectors are very effective - a bit too good when it is very hot, but I'd trade that for the protection they give at 4500m or in Patagonia.
[Barkbuster abuse]
Headlight Guard (Touratech, steel mesh). The Touratech grill-style guard came with the bike and I thought it was a bit of overkill, until a 4x4 passed me at speed and threw up a big stone, right on to the headlight guard. Very glad I had it. (The stone then ricocheted into the hand guard, convincing me of the importance of them too.)
Centre Stand (SW Motech). Weight v convenience. It has certainly made life a lot easier when working on the bike, repairing punctures etc. If I had a lighter bike and really wanted to stay light, I'd go without and accept the inconvenience. But the Ten is heavy enough to justify the extra weight for convenience. The SW Motech stand has been good, although the little side arm used for deploying it sits irritatingly under the pillion foot peg - mod needed.
[Annoyingly hidden under the pillion peg, difficult to deploy with your foot]
Camel Toe (Touratech). Essential out here to stop the bike toppling over on soft ground. The TT one has proven robust.
Heated Grips (Oxford Hot Grips). A God-send in Patagonia and on the Altiplano - 40 quid very well spent indeed. Combined with Storm hand guards on the Barkbusters, they mean I can ride in my Klim Dakar gloves even when it gets chilly - so no need to stop and change gloves when the temperature drops in the mountains. I bought the old version of the Hot Grips on eBay for half the price of the new ones, and they haven't given me any problems (and they are hot!).
Pannier Frames (Touratech). They've held up better than the Zega panniers that used to be attached to them - one of them came off in Bolivia and was never seen again! They seem pretty sturdy, handling two relatively heavy aluminium panniers on several thousand km of rough roads with no apparent damage, and definitely limited damage to the bike when I was rear-ended by a Honda.
Luggage Rack (Touratech). Big, stable, lots of options for strap positioning - does a good job.
GPS Mount (Touratech) and Zumo 660. Mounted on the mounting bar above the clocks, the GPS in an ideal place for visibility. But this set-up has one big disadvantage - the additional weight, high and rearwards of the headlamp stay on which it is attached, increases the load on the stay when driving for prolonged periods on the dirt. The stay has sheered three times, despite reinforcement at the base. I now have a new stay which is even more heavily reinforced, but I am going to cut the mount down so that the GPS sits lower and less rearwards - hopefully putting less stress on the stay.
Aux / Backup Lighting (X-Vision 5 Inch Xmitter, Narrow Beam, from Adventure Spec). Super bright, narrow beam. I have them wired into my main beam, which gives me ample light (whereas the main beam on its own is crap). Initially it was mounted on the bottom of the headlight stay, but now it is upside down on the towing hook, which works really well. My logic for fitting one on was recently validated: my main lights packed up, and the X-Vision provided me with both light and the means to be seen. I think the optimal set up with an HID dip beam is to rewire so that on flicking to main beam, the HID remains on and the X-vision supplements it, leaving out the stock main beam altogether. This will give excellent near and far range illumination, and avoid the momentary darkness when flicking back from main beam to a now cold HID.
[X-Vision mounted on the towing hook]
12V Power Socket (Touratech). Essential. I charge my phone and iPad (stored inside my tank bag) on the move, and run my electric pump off it.
Engine Guard Toolbox (Touratech). I was hesitant about getting one of these, but when I came back to UK briefly after 6 months I got one and am really pleased I did. It's not the best design for ease of access (I've seen a neat mod on one of the forums to allow the lid to open more fully instead of knocking up against the headers), but it means I can keep some essential tools on the bike at all times, and more importantly I can get some of the small heavy items like spare brakepads and my chain breaker down low. It seems to be handling the knocks fine. The lock, like all TT locks, is a bit cheap.
Break Fluid Reservoir Cover (Touratech). On the bike when I got it, but not sure it serves much purpose.
Manifold Middle Heat-shield Plate (Touratech). As above, but this one probably does help a bit to prevent melting your trousers.
Pinion Gear Guard (Touratech). It was a pain in the ass when my chain jumped off the rear sprocket in a crash and jammed up in the front sprocket, but maybe it actually limited the damage.
[Manifold and pinion guards]
Bar Risers (Wirtz, from Adventure Spec). Actually these are primarily adaptors, necessary for the 28mm Renthal Fatbar. But they also raise by 20mm, which I need to be comfortable standing on the pegs. Really comfortable riding position now.