Suzuki: steering vibration at 70 mph, wheel bearing, merry chase

Question
My Grand Vitara steering shakes at 70 mph, and the car
overall feels unstable.
This is a year 2000 4WD, Auto Transmission Model.
Have been to three workshops for a problem definition,got
the alignment and wheel balancing done, but has not helped
at 70 mph and above. The tyres are new.
Was recommended for a Drive shaft balancing at one of the
shops.
Is that a valid recommendation, will it really help and how
costly can this whole exercise be?

Answer
There are two possibilities that most repair shops could miss.  One is water in the tires (it can change the tire balance significantly), the other is wheel bearing and/or suspension play.  Both have led me on a merry chase on my own vehicles in the past.
scotty