I'd say it's worth it- the charging issue is not too big of a deal, common problem with GS's. Worse case you have to replace the stator and or the regulator/rectifier, $200-250 if both are bad. Check out
http://www.thegsresources.com for great info. The stator pages in the garage section tell you how to diagnose the charging issue. I just sold a 1980 GS850 to raise $$ to fix my Cb550- would have kept it otherwise.