An Emerson custom bought from one of his lotteries is basically guaranteed to resell for significantly higher than purchase price if bought that way. The secondary market is ridiculous with how much they fetch, but the only way to get a real deal is direct from the maker, which requires some luck. There are other makers like this that you could look into.
Problem is no one knows if something will suddenly not be popular, just because Emerson's have been very popular for a while doesn't mean tomorrow for whatever reason they won't be worth squat. Knives are really not great investments.