Maintenance of Fork springs on Marzocchi Bomber Dirt Jumper
Deciding whether or not to replace the fork or to service it, is a question only you can answer. You'll have to calculate how much it will cost to repair vs how much a new fork is. Take into consideration that your fork is a decade old now and that the chances of it breaking will only increase as time goes on. Parts will also be hard to find.

If the springs are worn, you will most likely notice changes in the compression and rebound characteristics of the fork. A worn spring doesn't mean that something else will break.

Yes, you can replace the springs yourself on most forks. Chances are, if you can buy/find a spring, you will be able to replace it. You might need a large socket/wrench for the top cap, but you should be able to do it yourself.