1.) Why should anyone seek enlightenment? To echo Shinichi: because the urge is there. If there isn't one, then it'd be a pointless endeavor.
2.) How would enlightenment improve one's life, afterlife, or the ability to be of service to others? This is simply my experience, but since becoming interested in this whole enlightenment thing, I've had increased appreciation for a great many things I would never notice had I not taken the time to learn how to notice them. I'm not sure if I've helped another living soul yet with what little I've gleaned, but the awareness extends to my interactions with others, and it shapes with how I interact with them. On a personal and social level, it's helped me better deal with my over zealous Christian mother and my sister, who is her little protege, in a loving peaceful way. Where once there were fights and hurt feelings, there is now understanding.
3.) How would it be more noble to spend hours in meditation seeking enlightenment, rather than spending this time making the world a better place? I think this bears defining of what you feel is actively making the world a better place. Peaceful protesting? Service to those less fortunate through volunteer work? Third world country volunteering? Missionary work? Donations to fundraisers that go to a good cause? Working mundane jobs to fund those donations? Working and being a good, contributing tax payer to the local government, who then sends that money into social programs and healthcare systems? Tithing to religious sects, so that they in turn can spread the word and fund missionary work?
It also considers what you mean by spending hours--let's say you spend an hour a day in meditation; are you still capable of getting your work done within the day? Are you socializing with your family, contributing your part? Then an hour doesn't seem like a big deal, but adds up to quite a sum of hours at the end of the year. Or are you speaking extreme cases where people go for weeks on their own little spiritual journey? Either way, if that hour a day, or a concentrated amount of time gives you the inspiration and motivation you need to create good in the world in any significant way you're capable of, then it's well justified. If it gives you the compassion to give to those who are in need, if it gives the ability to answer questions from personal experience and contribute to another's growth, even if it gives you just a little bit of quiet in your mind so that you can rewind and be more affable and loving to those who love you in return and even those who don't, then it's justified.
4.) Since we're here, why not enjoy the things which can only be enjoyed here, and let us enjoy the spiritual worlds after death? I think this question and my answers are closely tied in with the first and second; for people who choose to pursue enlightenment, it's because they want to. It's because they find joy in it. I find that enlightenment is not about enriching the afterlife, but this life we have in the here and now. I think it helps you to better understand the other things you enjoy, why you enjoy them, and how to find even more fulfilling pursuits.