I guess the key question is what are your goals? Your goals and expenses determine what you should do and whether it is worth your time.
There are a number of key pieces to an optimal web site. Take a peek at
25 things your web site should have. This is a good start to helping you understand what your web site should be.
Also, you do have some validation issues that need to be addressed to clean up your web site. Visit
The W3C Markup Validation Service to see what those issues are.