Here's the thing: choose the best spec for YOU. If you spec what you want you start to realize you fall into the spec thats best for you. Discover your class, dont play it according to a guide. That was part of the magic of vanilla, most of us didnt know a damn thing about what we were doing for a good few months.
There are so many different playstyles for Warlock and the real benefit of a Vanilla server is that you have the flexibility to design your own spec. Many locks in vanilla had hybrid builds, and they were all acceptable as long as the person knew how to play them.
Part of what sucks about retail wow these days is how cookie cutter it's become. The lack of differentiation made the entire player base have similar builds.
Back in my vanilla raiding days we had 6 raid locks that each had different specs. They all fulfilled a role and a function during raids. We all talked about the class and our specs, who was better for which roles, who would do which curses, and who currently had SS's up and learned a lot from each other, which informed some of our tweaks to builds. Heck, at some points we even factored DPS output of DoTs vs DD spells and figured out that dotting trash was a waste of mana based on the time it took to dps them down with the raid. It also forced us to optimize DPS output based on debuff limits.
Best thing I can suggest is to talk to other locks. You learn the most from other guys who play your class.