Call me the contrarian here. I'm on my 4th RT. I love them! If I were looking now, knowing what I know, I would find a well maintained '05 to '08. Here's why:
1. Surging, throttle bodies and final drive problems on 1100s. If you can find a dual-plugged 1100, maybe go that way, but these bikes are never in tune. A lot of them surged at just under 3,000 RPMs to about 3400. This is a very common running area and it drove me nuts. I did a lot of mods to mine to solve it...They all cost me money and time. I lucked out and ordered up a "spline lube" at the right time from the dealer. They found leaking output bearing, a clutch started to get wet and other problems....all replaced under warranty. You won't find that anymore because...no warranty. It's a big job to fix this stuff and the parts are expensive.
2. 1100 Fairings are a PITA to remove and install. If you buy SS screws and do everything in proper order, it's still a PITA but less so.
3. Get an 1100 with an aftermarket seat. The stock seat will put your private parts to sleep within 50 miles. More expense.
4. Get an 1100 with a good touring windscreen...The aeroflow "Tall" for those bikes was my favorite.
1. Servo brakes on these bikes are abominable. You can not stop smoothly with these brakes. After 2 years, I was still trying to do that consistently...can't be done...terrible. And...when the bike is turned off, the brakes almost don't work at all...so pushing it around the garage is a challenge.
2. Surging is solved with dual plug models. Surging is worse with single-plug early models...so make sure you get dual plugs. However, the throttle bodies are still made by Bing...and that means that the little axles wear out and allow air to seep in. When you have air leaking in, you can't really tune the throttle bodies for smooth running at all speeds. This gets pretty frustrating after going to all the work of a tune.
3. Rear brake is linked. You can't apply the rear brakes without applying the fronts. Not a big deal unless you're going downhill on soft ground at a rally...Ask me how I know!
4. Fairing still a PITA...but better.
5. In spite of and extra 50cc and dual plugs, there is no more performance from the 1150. They de-tuned it for emissions reasons. They run a bit hotter...but have better oil coolers.
6. Aftermarket seat and screen highly recommended. I used the ones from my 1100.
7. Original shocks aren't the best. Find one with Ohlins or Wilburs? I transferred the Ohlins from my 1100 to my 1150...paid a bit extra for a couple new bits on them...and they converted. Worked well.
8. Always change brake fluid on any of these bikes every year or every 2 years if you have teflon braided brake lines. You do not want ABS problems. This was the one thing I always had the dealer do. I've never had an ABS problem on any of the 4 RTs.
9. Always use reputable premium fuel in these bikes. I've never had a fuel gage problem on any of my 4 RTs...and this is supposedly common on some years. Fuel strip? Anyway, put good fuel in and avoid this and other issues.
1. I loved mine. Put 90K on it and it's still going strong under new ownership...Minimum maintenance. Yes, you have to adjust valves but it's not difficult to learn. There are videos for sale that cover all the maintenance. Do a finiky great job at the valves and you don't need to touch the throttle bodies at all...or remove fairings at all. This is just so much easier.
2. Engine is stronger and smoother.
3. Handling is improved.
4. Center of Gravity is lower and it's just easier to operate at low speeds.
5. The locks! 1100 and 1150 have a lock system that requires you to lock the bags in order to close them securely. This is a PITA for packing the bike. You forget something, you have to find the key...which lock did I leave it in? The 1200 allows you to latch the bags unlocked. I ride all day unlocked, then pull my liners out and lock the bags at night with whatever I want to keep on the bike. This is really sea-change for the better.
6. Bags hold a bit more.
7. Again, get aftermarket screen I like CeeBailey flip-up "tall" (not the Euro version, not "tall-wide".) You may want to replace the arms that hold the windscreen with aftermarket ones. I went through a bunch of OEM ones. They would break on the expressways in the wind. This solves it. I got new uppers and lowers and never had another issue.
8. I got my Wilburs shocks rebuilt by Beemershop after a couple years of putting up with a not great setup from the NJ guys. When they came back, they were GREAT.
The 1100/1150 shocks will not fit the 1200. Strongly recommend Beemershop because they know how to set them up properly.
9. RT's are tough on rear tires. When they get flat in the middle, handling is affected negatively. I found that Metzler tires handle best on curvy roads, but if you live in the flat part of the country and every decent road is 200 miles away, you need something that will hold up to straight line miles without squaring. Michelin Pilot Road 3 or 4 have worked really well for this. I haven't tried 5s yet. Point is, they have hard rubber in the center and softer outside with a good belt construction. I'm not a tire industry expert, but I've gotten extremely good life out of these and they are still decent when they get worn a bit. Metzler are favorite if you live near the curves and wear the sides out before the centers. I'm jealous!
10. With all these little problems, you'd think I'd be negative on BMW bikes. I'm definitely not. Any of these bikes are worth the trouble. They are just lovely to ride. They handle extremely well and have a lot of engine braking available that can be used to help you around corners and let you change your line mid-turn if you need to. This gives great confidence in the bike. The GS is the same. Both are wonderful machines that really communicate with the rider and are comfortable enough for long distances. Of them all though, I think the early 1200 bikes represent the best overall value. Having a budget should include maintenance and repair costs. Both will be lower on the 1200.
All that being said, you really need to buy from someone who has taken care of their bike. This doesn't mean shiny, this means maintenance has been done. It's not got the original brake fluid. There aren't broken things. They were stored properly with fresh oil in them. I'd also shop for a bike that was ridden and has good accessories. Some, like a decent aftermarket seat and a good touring windscreen, are required equipment, in my mind. Aftermarket shocks are a huge plus. They can be rebuilt indefinitely. Shop well. There are some real bargains out there. Dealers around here are bulging at the seams with really nice used BMWs. The new liquid cooled bikes are very popular. Lots of trade-ins around. Get the history and know the previous owner...or budget some money to get things put right.