A lot depends on what country you're in. In the US my guess would be not much resale value at all base on the fact it isn't a very popular phone. I've already seen some listed on Craigslist for $430 which is the same price I sold my HTC One for.
Another way to look at it is looking at the Optimus G and G Pro and compare them to its predecessor the Galaxy s3 and Note 2 and you will definitely see a price difference on eBay.
Me personally, I don't care about resale value because with T-Mobile's "Jump" upgrade program, I'll be able to sell my phone to them after 6 months regardless of what I owe on it and upgrade to the next big thing.