Hi, well like you I have had 32 bikes to date 5 BMW's including a K1200RS, Triumphs, Suzuki's, Honda's, Yamaha's etc the 650 v-strom is the best all round bike I have ever had and comfortable, but I do not do much motorway work these days as I live in Norfolk where there are no motorways, but having said that it should handle that without a problem, but I think you will have to assess your use and decide which is the main use motorway or traffic, I do not think you will find a better bike for traffic use, but if your main use is the motorway perhaps the 1000 would suit better ? try and arrange a test ride on both to help you make up your mind,
re corrosion I do not think the v-strom is any worse than a Honda or a BMW for that matter, a good dose of a protective would sort out any problems that might occur for the winter.