I think the most important thing leading up to the draft is staying current on injuries and training camp battles. When I first started playing fantasy football, I went the route of complex formulas to try to predict future production, but in the end you're right it isn't worth the effort. In the NFL things are so fluid, that the only statistics I consider are fantasy point output from the previous season, using my scoring rules. That number gives me a start point to begin manipulating my rankings.
I definitely think its important to have a comprehensive cheat sheet with bye weeks, and you should vet all players for about a week leading up to your draft to be sure someone hasn't fallen off the map due to injury or lost their spot on the depth chart to someone else. After that, just be smart and go with your gut. It's also important to remember that, while the draft is definitely critical to your fantasy success, your actions during the season are just as important. A good owner can recover from a poor draft if they're worth their salt. Save your stamina because the season is a marathon, not a sprint.
So, in closing, don't overdue it when preparing for your draft. At the same time, don't rely on a random cheat sheet you found online to assist you, then end up making a stupid mistake because that cheat sheet was only updated a month before your draft. I can live with some players on my roster not living up to expectations, but it'd be harder to stomach a poor team resulting from laziness in draft preparation. Do enough to put yourself in a position for success.