Hi Medved,
While there is much good information on this thread about how and where to lead the vang control line, I think your initial question was more like "what would sailors on this forum, with considerable C34 sailing experience most recommend if they were purchasing new sails, standing rigging, and running rigging"? Let's take these one at a time.
My long departed and very beloved father used to say "The easiest thing in the world is to spend someone else's money". Thus, one might recommend carbon fiber sails, rod or even carbon fiber standing rigging, and all Vectran cored running rigging. One could quickly spend more money in these three areas alone than the market value of an entire 20 - 30 year old C34!
So, I will go in the other direction. How can one achieve the most "bang for the buck"?
Regarding standing rigging, I and I believe most others would say that for anything except a full out racing machine, conventional 19 strand SS wire rope will provide the greatest "bang for the buck", and if checked periodically, not grossly overstressed by sailing in a hurricane, and maintained properly, should last for a minimum of 15 years and probably even longer. The standing rigging on Pleiades is inspected every other year, has ZERO "fishooks", zero rust, is never sailed in winds over 40 knots, and is now 30 years old. I probably will upgrade to all new standing rigging next year - just because at 31 years we are probably dancing on thin ice.
Regarding running rigging, again unless you plan to do a lot of racing, conventional Dacron (viz. polyester) line works fine for most applications. One "modest upgrade" I might heartily suggest is the use of Regatta Braid for the jib sheets and main sheet, since I absolutely detest "hockles" in running rigging, and lines like "Sta-Set" are very prone to hockling (i.e. twisting itself into a pretzel that will then not pass through a fairlead, or a self-tailer on a winch). Regatta Braid, on the other hand almost never hockles! Also, if your budget will allow, I definitely would look into a bit more exotic lines with significantly lower stretch for the main & jib halyards (some stretch in a spinnaker halyard is OK to minimize shock loads when the chute suddenly re-fills in a fresh gust of wind). I got really tired of having to regularly re-tension the former Sta-Set X halyards after luff wrinkles would re-appear as the wind increased. I switched to a Vectran cored line by Yale about five years ago. The extra cost was probably $200, but it is now an absolute joy to apply winch tension to the main and jib and KNOW that there will not be a bunch of luff wrinkles 15 minutes later.
By far, the biggest impact - and the biggest cost - will be a new suit of sails. Here the influence of local conditions will be significant. In predominantly lighter air areas you may want a bit larger headsail, while in windier areas a smaller headsail is better IMHO. Tacking is much easier and faster with a smaller headsail, especially so in heavier winds and with minimal crew. I definitely would recommend a loose footed mainsail (better sail shape down near the boom, and much easier to secure reef ties around the foot of the mainsail when reefing), as well as four full length battens (again, better sail shape head to foot). A square top or more roach at the leech might be nice if you were racing, but they add expense, complexity, and only modest gains in performance. Finally, I would seriously recommend a minimum sail cloth weight of 7 oz. / square yard, and perhaps even 8 oz. Lighter weight is fine for very light winds, but it only takes one sail at high wind speed (intentional or unintentional) to pretty much permanently "blow-out" a sails shape.
As a physicist, I always used to say "angular momentum, not difference of opinion actually makes the world go around", but indeed you will get different opinions from different sailors, in different sailing areas. Hopefully, my comments above will help you make some important decisions. If you replace all three the performance of your C34 will be significantly improved, but I fully understand that within reasonable budget constraints, you really want to "get it right the first time". All the best in your quest.
Fair winds & following seas,
Paul
1990 C34 - 1068,
Tall Rig, Full Keel.