I have used Kaplan books from a while ago that did not have probability/combinations/permutations/statistics, etc and I did Ok as well. I got one probability question and bombed it on the GMAT- spent 4 minutes solving and did not find the answer. It was a fairly simple one I later realized.
I have to say, I wish i answered it but I guess I'll settle with Q49

My opinion would be that if you are short on time, absolutely put all the time into Arithmetic - half the questions rely on it.
If you have time, harder subjects are worth it as well since they often rely on easier concepts to solve, thus you are practicing on several levels, but that's me. I tried to do everything I could to prepare.