I wouldn't say that they are elitists so much as perfectionists.
The 501st and Rebel Legion have an image to uphold and are very much in the public eye given their direct affiliation with official Star Wars events, so they want their members to have the best costumes. They are picky because they HAVE to be in order to maintain that relationship and enjoy their official sanctioning by Lucasfilm.
As a member of The RPF, I feel I can say that they are not elitist at all. They are very welcoming to newcomers and are perfectly willing to offer advice, but you have to be wiling to do the research and put in the hours to do it. They aren't going to spoon feed it to you. Many of the members are industry professionals and have LOTS of experience making professional costumes and props actually used in Hollywood. Even Adam Savage is a member (though he rarely posts). This level of costuming and prop making is why they are perfectionists. Their careers depend on it, and "good enough" just isn't going to cut it. That said, most of the members, like myself, do it for fun and are also willing to help each other out.
Sadly I have to kinda partly disagree with you- you WILL run into elitists in clubs like these- but even local small clubs (of which I am part of) get the same rubbish- and sometimes those elitists are NOT the best costumes or costumers. But as Jev said you do have to take into account that any group that has gone as far as becoming a proper club do have an image to uphold and standards to set. They have a reputation to uphold. They can't just let any rag tag costume in. This doesn't mean that because YOUR costume doesn't meet standards that it isn't good. Far far from it! I've seen some amazing outfits that would never make the cut in a club like that but it doesn't make them any less impressive- you don't need to be screen accurate to look the part and look good, nor do you need master costume making abilities!
Those clubs
have to have very high standards and as a result if you want to join one of these clubs you have to be prepared to take that into consideration- it will instantly shoot your costume price up. My first Jedi cost me like... I dunno maybe 40 or 50 bucks AUD for tunic, pants, robe, tabard and obi, using boots, belt etc I already had. It did the job and looked the part. I am currently making my SWTOR costume for RL entry and it has to be screen accurate- my current outfits do NOT meet standards. I'm expecting to spend at least $100- $150 on material alone, my boots cost me $50 (cheapest part of the whole thing!) and I bought a spare set as well, my belt is likely gonna be anywhere from $100-$300 depending on who I buy it through because it HAS to be custom made, and I'm going to have to get some 3D printing done for it as well.
This is an issue that the 405th Halo costuming club is running into- they are progressing from a forum with costuming members to a proper recognised club. There will have to be rules and standards, which they are still working on though they are looking at having different classes of costume standard so that those who make cheaper/ quicker costumes rather than 100% screen accurate aren't excluded. This will also upset some people. That is what happens. Even a local costuming club I'm part of has an approval process with charity approved and social approved costumes, because they have a reputation to keep and have to be somewhat professional. If you want to be invited back to events and expand out to new events you
have to be somewhat professional.
Please keep all that in mind when you are dealing with people in those clubs. I try not to be an elitist but I do strive for perfection, as much as I can. This doesn't mean I think the costume you've put all the time and effort into to make it look great is automatically bad because it isn't screen accurate. If you ask me questions about how it could be more screen accurate then I will give you opinions with what limited knowledge I have, but I won't automatically dis you for it
I've seen some great basic or simple costumes that their simplicity is what makes them so awesome.
I will add an extra note to the costume designing/ creating process:
You have the right to make a character/ costume how
you want. This includes your own intepretations on it- whether that be a bright pink storm trooper, or you've decided to have your Jedi with a purple robe, or a femmeplay of a male character- or even a male playing a female character! Just keep in mind the more you deviate from 'original' and the more you customise, the less recognisable you will be (and possibly the more snippy remarks and frowns you will get). Also if you are costuming a lesser known character especially from the huge field of anime or comic books then the general public are not going to know who you are. We Halo Spartans have been called everything from robots, to stormtroopers, to aliens, to Power Rangers, to space troopers, and even weirder things than that! That doesn't mean there is anything wrong with your costume BUT you must be prepared to accept that if you aren't as recognisable you may not get the attention you think you deserve.
Im sure I shall also be yelled at for this but women (or men even): if you decide to wear a skimpy costume then you must be prepared that you will get comments and looks as a result of it. People will notice if some body parts have more showing than covered. Again it is your right, and it is also your right that people don't use your outfit as an excuse to be derogatory or do anything to you as a result- whether that is leering or getting touchy feely. It is all harassment regardless. Put in short however, if you aren't comfortable with the idea of people taking pictures of you in that outfit and those pictures ending up online then you shouldn't be wearing it at an event. Also make sure that you keep your costume 'appropriate'. Keep it PG if you are in public
This can extend to 'normal' costumes as well- some people might find your costume offensive (whether fully covered or not). You have to consider this when going to a particular event. We had a guy turn up in a Nazi uniform one time to a charity event and we had a few members of the public very offended by this. Context is everything- if we had a Captain America and his costume was Red Skull then it would have been entirely different, even though it would have only been a case of changing a few badges over. Similarly, characters from particularly violent movies/ video games etc are often not allowed at kid's charity events because a) not recognisable and b) not suitable.
I would LOVE to design a costume around one of my kilts.
That could be a handy skill to have
Actually there is a kilted division in the RL
It's a bit of a 'fun' aside thing
In saying that there is actually also a RL cheerleaders division.