You get at least four things from WCs: FIE points, US points, high level competition experience, and travel.
I'm starting with the least fencing oriented aspect of this page to get it out of the way. A lot of the experience you gain by going to WCs is in how to handle traveling. WCs are held in wild and remote parts of the world, as well as in European capitals. If you have ever had the urge to see any of these places and can take even one extra day to do some sightseeing, this is a great opportunity. But don't think it will be all fun. Traveling is hard. Your flight is delayed, your baggage gets lost, your hotel sold your room to someone else, you can't find your way around the city, and the time difference has you sleeping all day and watching TV in a language you don't understand all night. To top it off you probably have work to get done on your laptop but you didn't bring and can't find a power converter.
Seeing foreign cities can be fun, interesting, and educational, but it's rarely as much fun or as interesting or educational as the people you left behind in the US will believe. But take pictures anyway, because when you get home you will probably wish you were still overseas.
Your first international competition is confusing, disorienting, and the level of fencing is very high. Getting used to the kind of things that happen at those events helps you stay focused when getting a good result is important.
Fencing strong fencers and seeing different styles of fencing is the core of competition experience. You can only get it by going there and competing. And the more of it you have, the better your fencing will be.
If you make the top 64, you get FIE points. The higher your place, the more points you get. Therefore, the weaker the competition is the more points you will get on average. The formula for your world ranking limits you to a maximum of 6 results total, with no more than 4 from one zone. If you want to get the best possible ranking, you should go to the weaker WCs. These won't be the ones in Europe or the ones with team events attached. The US designation system encourages you to go to the European events, and the USFA may help pay your way to a team event. Conflicting input? Yes.
A higher world ranking directly benefits you in WCs. The higher your seed, the easier your pool. If your seed is high enough, you get a bye to the second day. There are European fencers who spend all season trying to improve their world ranking. Your world ranking should be a consideration when you pick which events to attend.
If the SF is 2.0 or higher and you finish in the 64 you get 200 points. If you make the 32 or higher in any WC, there is a table in the Athlete's Handbook which specifies how many points you earn, multiplied by the SF or 2.0, whichever is lower. For designated events with a SF of 1.0 or higher these are add-on, aka "group II" points (to a maximum of 5 results), for the others they are replacement, aka "group I" points. (These rules apply only for Men's Epee in 2003 - the other 5 weapons have slightly different rules.)
Maximizing the points you get in a season is an interesting topic. You need to go to tournaments with a SF low enough so you can get a good place, but not so low it drains away the points with a low multiplier.
Very very roughly, if you can beat someone with a world ranking of T or worse, at an event with attendance P you will finish in about place P*T. (More accurately, your result gets better as your world ranking gets better, as detailed elsewhere.) Look at the table for international points in the Athlete's Handbook, and you see that the number of points you get drops greatly after 4th, 8th, 12th, 24th, 32nd and of course 64th. Figure out what the SF will be in a tournament where you are each of those places by taking that place, dividing by T and multiplying by 4. Multiply the points for those places by its SF and see what gives you the best result.
If your `T' is 32 or better, you should go to tournaments with a SF as close to 2.0 as possible. If your T is between 32 and 128, you will do the best at tournaments with SFs between 1.0 and 2.0. If your T is not as good as 128 you shouldn't be going to WCs with the intent of earning US points.
It should be easy for anyone going to WCs to get good enough replacement points this year, since we have 4 national events and only the best 2 count. The only US points gained from WCs with a SF under 1.0 are replacement points, so you don't need to consider those except to improve your world ranking.
Going to a WC with a SF of 4.0 guarantees you a worse finish than one with a SF of 2.0, but the multiplier is capped at 2.0. So there is no reason to favor the strong European WCs. Anyone going to Heidenheim or Paris doesn't understand the system.
This leaves only those with SFs between 1.0 and 2.0, or a little above 2.0.
You should understand how important your world ranking is.