Newbee, a few years ago I asked this exact question to Rabbi Dovid Gottlieb of Yeshivas Ohr Somayach via email.
Me: “Why do we want moshiach? It’s true that we will enjoy a closer relationship with Hashem, and that we’ll be able to feel and see His presence, and that there will be an end to much of the suffering around the world, but what about the effect on our freewill? Won’t it become less of a challenge for everyone to do mitzvos, and thus we won’t really be able to earn the greatest good? It seems like we would be better off if there was no such thing as moshiach, and the world would just continue forever in the state that we’re in of not knowing 100% whether Hashem exists and having to struggle to do the mitzvos.”
Another idea that occurred to me is this: Having a deadline other than death serves as further motivation to live up to our highest potential now, today, and not wait until we get older. Also, Hashem is perfectly fair, so when moshiach does come and you get “short-changed” by missing out on years when you could have been earning, you wont really be short-changed because Hashem knows everything and will reward us according to what we would have done had moshiach not come.
So there are two approaches, hopefully at least one of them is helpful