Time dilation is both simple and complex. For those with a mathematical bent, time slows down as √(1-(v^2/c^2)), where v is your velocity in your chosen frame of reference and c is the speed of light. But no, if you experience one subjective year during a spaceflight that lasts 100 years as viewed from Earth's reference frame, you don't get any more work done. You have literally and truly lived only one year, and perceived yourself as moving and working at normal speed, while a whole century passed back on Earth.
Aliens. It's hard to make any definitive statements about them, other than "we haven't seen them and we haven't heard them". If technological civilizations are widely separated and interstellar travel is really as hard as we currently think, then this result should not surprise us. But the galaxy does seem to be chock full of places where they could exist. Intelligent aliens are perfectly plausible until you put on a tinfoil hat and start arguing that They Are Walking Among Us. Nope. If they exist, they're either very far away, or they're at a stage of technological development where we can't detect them across interstellar distances.
I'm not at all sure what you mean by "they will be at a different stage of evolution than we expect". Evolution isn't some 12-step program that takes you from nonliving chemicals to starship-building sentients along some set course, so it's really impossible to expect anything in particular. You can speak metaphorically of important "stages" (endosymbiosis leading to the rise of eukaryotes; oxygenic photosynthesis; multicellularity), but none of those developments is preordained. And our sense of what is "important" is biased by the fact that we are multicellular oxygen-breathing eukaryotes.
But anyway, interstellar travel looks to be mind-bogglingly costly and difficult. If it happens at all, it's going to be done as one-shot colonization missions over distances of only a few light-years, to planets that have been detected remotely and characterized as life-bearing before the journey begins. You can't expect alien anthropologists or explorers or traders to drop by Earth for a visit under those conditions. I'm pretty confident that your friend will never meet an alien, although I wouldn't rule out the possibility that we will detect signals from an alien civilization. And that could happen tomorrow.
There may indeed be a narrow window of opportunity for sending out an interstellar mission. It's a matter of having the necessary tech, plus enough surplus material and energy resources to throw behind the project. All indications on Earth right now are that we're on the verge of having the tech, but we're also on the verge of a resource crisis and a population/tech crash. Our current oil-based civilization doesn't look viable (let alone sustainable) past the middle of this century, and we haven't even committed the minor resources needed to send a mission to Mars. You can forget about going to Alpha Centauri. Alien civilizations will be subject to the same physical constraints as we are, and are likely to find themselves in the same situation. And maybe that's why this corner of the galaxy feels so empty and silent.
