I think in your post you referring to the United Visa Club card that gives you United Club membership. The annual fee is just shy of $500 per year. It may be worth it if you would want to access the lounges during your domestic flying.
You can go to the United web site or to the Wiki associated with this United forum to learn more about the benefits of the various levels of elite status with United, but in short, the chances of an upgrade to first class depend on a combination of elite status and how much you paid for the ticket and of course whether United was able to sell the seats in first class via offers to upgrade to check in to flyers with no status.
Otherwise, with elite status you get priority boarding, and check in. Also, once you have gold status with United, you get free lounge access on all international itineraries. You can also access any Star Alliance Gold lounge when traveling overseas.
There are other benefits to status, but like I said, check out the United web site or this forum for more details.