I rode an '80 Suzuki GS450L for many years, it was my first new street bike. Sadly, there is really nothing out there today to compare it to. Adventure bikes are too big and top heavy, you feel like you are sitting on top of them. Sportbikes are nothing but torture devices, great for the track, or a fast run up a curvy mountain road, but certainly not long distance. Todays cruisers are seriously down on power from late '70s/early '80s cruisers, but are still probably the best way to go. They will not be light and nimble like your GS400. Even a V-Star 650 is a big heavy bike, but slow. If you fit it, and don't need a lot of power, the S40 is a very good choice. It is still air cooled and carbed, so there is very little to go wrong with it. But it will not feel like that GS400. I have a Vulcan 750, bought new in '02, and currently have 75,000 miles on it. It has been a good bike, and has taken me all over the country, it has plenty of power for a 750, but it is not as maintenance free as many people think. I would prefer to maintain a chain drive than tear the whole rear end out of the Vulcan every 10,000 miles to maintain the shaft drive.
I hate to say it, because I think they are the ugliest bikes on earth, but a new CB500 might ride more like the GS400 than anything else. But I just can't get past it's looks. I want a motorcycle not a spaceship.
EDIT: One bike that might be a good replacement for the GS400, still looks like a motorcycle, and is definitely capable of long distance highway travel is the Kawasaki Vulcan 500. It is a liquid cooled 500cc parallel twin that dates back to 1985, and was the replacement for the 454LTD, which was a replacement for the 440 LTD. It puts out over 50 hp, and is very comfortable. It's no longer available new, but it was made through '09, and there are a lot of nice ones still out there.
2002 Vulcan 750, 2001 XT225
2008 Vino 125, 2009 Genuine Stella
2012 Zuma 125, 1980 Puch Newport moped
JerryH screwed with this post 12-25-2012 at 11:47 AM