I have owned my 1985 Vanagon GL for 30 years.  It is a 4 speed manual, tintop, with GoWesty 16" wheels, and has power steering.  I now have 273,000 miles.  I am planning on keeping if "forever".  I'm wondering...is there a rule of thumb regarding suspension components and when it might be wise to consider replacement of bushings, ball joints, and such?
I have only replaced the front and rear shocks; no other work has been done to the suspension.  I currently have no issues with vibrations or unusual tire wear.  The alignment is true, and the vehicle drives nicely.
I mostly drive highways and freeways.  I drive gently.  Only very occasionally on dirt roads, probably a total of 400 miles out of the 273,000.  Just like I did when I converted my perfectly running 1.9 to a 2.2 Subie engine, I tend to lean towards preventing problems when parts and service is "relatively" easy to do, rather than having much stress in 5-10 years from now.  Plus, the enjoyment of a stronger ride.  

Was wondering if you had any words of advise? 

Thanks,
RichSan Diego