Yes, it's important. Are there other things that are more important? Sure. Does that make first year any less important? No.
I don't know if people ask this question because they don't like studying as hard as it takes to do well or because they just hate the material or because they are doing poorly and need some solace, but no matter the reason, the fact remains that everything is actually important and there really aren't any shortcuts. People talk about this year or that year as more or less important, but the not-so-subtle presumption is that someone who does poorly in one year has the ability to do well in all the others. Sure, other things are valued more by PDs and other subjects are more likely to appear on boards, but the guy who can just squeak by one year and then crush it the next probably rides to class on a flying unicorn.
Be very careful not to construe the advice aimed at fourth year students as applying to first years. There's a huge difference between saying XYZ doesn't matter to a fourth year who has already demonstrated he did well in pretty much everything else, and a first year doing badly currently who may or may not actually turn things around. What I have seen typically goes like this:
1) Ms1 starts getting behind and getting lower grades; decides first year material isn't high yield enough to matter; plans to step it up Ms2
2) Ms2 guns hard for the first exam but does a lot worse than he thought (what, we were supposed to remember all that physio?), so decides M2 classes don't matter and plans to focus solely on Step 1
3) Assuming Ms2 passes his classes, he gets to study period and finds himself plateauing a good bit lower than he hoped.
4) Finally takes step 1 and does so-so on it. Decides he'll kill it 3rd year, take CK early, and maybe do some research to compensate.
5) Ms3 year starts and he treads water for a couple of weeks until he realizes that he can't manage to balance the shelf study with clinical time; misses honors either because of the shelf or because of evals; decides that only IM and Surgery really matter since they're the big ones everyone looks at.
6) Still ends up P/HP in IM and Surg
7) That research he planned to do really isn't going anywhere either, but he'll start working on that later....
I could go on and on. The point I'm beating to death is that importance is probably best talked about only in retrospect. For now, assume that everything matters.