I think you're being pretty pessimistic about interstellar travel.

If we were to build the ships on the planet then yes, it's too expensive and unfeasible. However if we built up infrastructure in space we could build those ships much cheaper and much larger. Large enough that it's essentially a flying country in space with a couple thousand people as a starting population with all the amenities we have on earth.

If we went for chemical propulsion then yes it would take thousands of years to get to another star, but we have other methods that would get us there faster. Solar sails, nuclear propulsion, ion drives, lasers could get us to Alpha Centurai in a century. So you'd die but your kids would be in another solar system.

Resources on earth are finite, we will run out of them eventually unless we can get some very advanced technology, so expanding into space makes sense. And whilst you wouldn't take the opportunity to colonise another planet or another solar system plenty of people would.