While Lp(a) is a possible marker for inflammation and heart disease it should be noted that it is that - a marker. From what I have read and seen I have not seen evidence of Lp(a) being a causal factor, only correlative: a symptom.
Trying to cover up a symptom will not really solve the root cause. For example, CRP is a marker for inflammation, but we need to look at what it really does which is bind to harmful material like oxidized LDL to make it more “visibile” to clearance pathways - in other words (just like macrophages and fever) it is a part of our immune system.
So lowering CRP alone may in fact do more harm than good, as opposed to targeting the root cause. It could very well be the same for Lp(a) wherein it serves some purpose in the body that we dont understand yet and it goes up as a protective response to the real problem. Fact is - we do not know yet. That is why I would hesitate with your suggestion to off the bat blindly lower it.
LDL and higher total cholesterol are also not causes of disease in themselves. If they were we would expect to see higher risk the higher they go, and higher all-cause mortality. But we don’t. In fact, for women, the higher the cholesterol the lower the all cause mortality.
As for niacin… one of the side effects is elevated blood glucose, which is not what you want when trying to prevent heart disease considering many heart attack patients have elevated hba1c and 3/4 (iirc) have some elevated diabetic marker like fasting insulin.
From what I have seen treating symptoms doesnt work. There was a new drug that they tested recently which blocked inflammation - a huge marker for atherosclerosis (for good reason). It lowered heart event risk by 1% (absolute) and all cause mortality did not change.
Based on everything I have seen - you must go after root causes for any disease to truly alter the risk of death long term.
Ivor Cummins quite effectively covers what these root causes are, and pretty much all of them can be changed.