Regardless of how wonderful vacations and Friday evenings and holidays feel, they wouldn't feel like anything if you didn't also have the opposite: hard work. If every day was Friday night, it would lose its magic quite quickly. Therefore, work has instrumental value in making you feel like you deserve that metaphorical Friday night.
Furthermore, work makes you feel like you've accomplished something. You're doing something meaningful, or leaving a mark or a legacy to live on after you die. You can go to bed happy at night, knowing you did something good. Therefore, work has intrinsic value as an end in itself. (You can also see this point of view as instrumental, since the end goal is your happiness, and working is just a tool to get there.)
Finally, working hard allows you to completely ignore any real issues that would become evident if you stopped busying yourself and stopped to think about what really goes on in your head when you're not doing anything. Work is a form of escapism: without anything to do, you'd go crazy. Therefore, work has instrumental value by giving you no time to occupy yourself with stupid, existential ideas that benefit no one.
Definition of hell is having nothing to do.
Definition of heaven is bliss, even if its ignorant.