I reckon it helps if you don't always think about films as having a goal or aim. One of the things I like about 2001 is that it's like a cinematic painting - it looks wonderful and conveys a general theme, rather than having a conventional beginning middle & end story. For me, the overall theme is rebirth - each time the monolith appears, the human race reinvents itself. I think that's what the foetus symbolises at the end. We think he's dying, he sees the monolith, and it signals another new beginning.
I think it's a mistake to view it with the expectation that you'll suddenly have some revelation. A good piece of artistic invention will invite different views on what it's about - I've just given my personal interpretation of it. Try to lose the idea that there's some hidden meaning you're missing, or that you're being thick, and instead just sit back and enjoy the ride. Maybe then you'll open up to my view of it or form one of your own.
On a side issue - what Dave does to get back on the ship when he finds himself locked out of the airlock is one of my favourite scenes ever, and I still can't work out how they achieved the visual effect but it's stunning.