Is it wrong of me to point out that your question is about a COSTUME and NOT a COSPLAY!
Costume (n.): An object of clothing to be worn.
Cosplay (v.): An activity where a person wears a costume.
To answer your question, In my opinion, keep both. Why would you get rid of something that you enjoy?
But you are not me. YOU are heading to college in 3 weeks. Your living situation will be "Variable" during the next 4 years, meaning: Don't try and carry around a bunch of junk. This includes, but not limited to costumes, models, furniture, sports equipment.
Sell them both. Both of these items are 100% replaceable at any future date, and can be reacquired after landing first job. I say this because over the years, it has become increasingly easy to find and make these items. 3D printing will evolve, and manufacturing replicas will be easier and cheaper.
20 years ago, I would not have thought that I could by a SS Millennium Falcon, AT-AT. or full size printed Iron Man suit, but today, I could have any of these items within 24 hrs.
Do you know what you will want in 4 years?? Neither do I.