fresh shocks definitely worth it
after 40 000 odd miles on the OP's bike, fresh shocks would be worth it.
myself, I went with Elka's after about the same mileage, but I expect any properly set up aftermarket would be fine - expect you'd have to be really racing to reach the full limits of any of the aftermarket shocks. For what it's worth the company I bought from warned about buying 'too much shock', lots of local suspension shops could rebuild your factory ones.
some of the quotes I saw were about $400 per shock for rebuilding...
the Elka's are 'harsh' especially if you're putting in long hours on smooth highway - there's no real softening them up, or it the handling becomes terrible...
'07 BMW R1200GS ADV (spring 2014)
'78 Yamaha DT 125
'76 Honda CB 400/4 (red)