To freshen up your ignition, you need some parts. Depending on what you're buying, you might need several hundred dollars worth of parts. But most ignition systems can be freshened for far less. If your mechanic has told you that your distributor is worn, a couple of things can be going on. First, the bushings in the distributor can wear out, allowing the shaft to wobble as it turns, which changes the timing of the spark. Secondly, the advance springs can wear out, changing the rate at which the spark timing advances as your engine revs up. Either way, if your distributor is worn, you can either have it rebuilt professionally or get a new one.
Spark Plugs and Plug Wires
You will need 8 spark plugs. I like NGK V-Power spark plugs. Don't be taken in by expensive platinum this or 4-way that - those features really don't help a spark plug do its job. Professionals like the NGK V-Power, and these plugs work great at a reasonable price. Just get the heat range and electrode design recommended for your engine.
If your plug wires are stiff or cracked, you'll also need a set of plug wires. Buy good wires from MSD, Accel, or Delco. Cheap plug wires won't last and may fall apart quickly. Universal wire sets may require you to assemble the wire ends, which is not good. I prefer the MSD plug wires - They're pre-cut and pre-assembled, and they're a snappy red color, so they look great.
Distributor Cap and Rotor
You should always replace your distributor cap and rotor as a pair, and they are generally sold in pairs for that reason. Even if the old ones look OK, it doesn't cost much to get a new set, and you can be sure that they're working at their best. Again, I like the MSD products, but the Delco or Accel products work fine.
Ignition Coil
Coils do not often go bad, but you can upgrade from the stock coil to a higher voltage unit. This gives your engine a stronger spark, which can help an old engine cope with oil consumption, reduce emissions, and help your car get started in the morning. I like the MSD and Accel upgrade coils.
Points and Condensor
Finally, if you have an older system, you'll want to replace your ignition points, These are spring-loaded electrical contacts that run on a cam that is part of the distributor shaft. As the points open, the coil loads up with electricity. When the points close and complete the circuit, the coil can release its charge through the distributor cap and rotor to a plug wire and ultimately, create a spark. Replacing points (and condensor, just in case) is a tricky business, because you have to set the working gap when the points are open. Set the gap too small and you get a weak spark. Set it too wide and you might not get any spark at all. Follow your service manual's instructions if your car has points.
High Energy Ignition (HEI) System
If you have an HEI system, you generally don't have to touch the HEI module. It works by spinning a magnet past the HEI module, and you can't adjust anything to do with it. However, once again you can upgrade to a better HEI module. The stock HEI module still uses a condensor (a little metal cylinder with a wire attached), while the replacements such as the MSD Ultimate HEI unit do not. This eliminates one more failure point from your ignition system, and the MSD unit also has an adjustable rev limiter built in, so you can guard against over-revving your engine.
What Will All This Cost?
If you buy an aftermarket kit that includes everything I described, you'll spend about $300. That will buy you the MSD Ultimate HEI kit with coil, cap, rotor, and HEI module, the MSD 8.5mm performance plug wires, and a set of NGK V-Power spark plugs. After that, you can get away with just changing your plugs for at least 50,000 miles, and the coil and HEI module should last indefinitely.
So now you know what you need to know to go shopping and get your ignition parts. Next, read up on how to install your new parts in your Corvette.