They are not usless and keep the chain tight. Without the guides the timing chain has slack and will, over time, grind down the cover and then you will have anti freeze all over the place. If it is your timing chain, you will notice the noise more when you start up your car and after long periods of driving. It is a much different sound than your lifters. The noise will also get louder over time.
Try putting more oil in (past the fill line) to quite the sound. This is only a quick fix. What I would do is if it is your chain that you are hearing, drive it till it breaks and have a sr ready. Its not worth fixing because of the time/ money it takes to get in there. I didnt read this whole thread but im sure its the one wannaskyline was talking about. In first diagram, # 15 is the one that broke on me and is the one that usually ppl have to replace.
Hope it helps. Moral of the story is, If its the timing chain, live with the sound and drive it till it dies and replace the engine. If its the lifters, put a little more oil in and caller a day. AFAIK this is also called the Ka tick and you will get used to it and its nothing to be alarmed…just maybe keep the high reving to a min.
EDIT: if you cant tell the difference, take the oil pan off and if there are a bunch of black plastic pieces in the pan, its your guide. Or you can go take it to a mechanic and he should be able to tell the difference.