I think its really hard to figure out which iems are improvements for your collection.
Since we are spoilt for choice this year especially for CHIFI, I can think of a few ways to see if certain releases/hypetrains are gonna be an upgrade to what you already have:
1) Wait a while for some reviews to filter out before jumping on new purchases. A lot of sets may be hyped in the prerelease phase by sponsored reviewers and such, but sooner or later more reviews will come out, especially from lay consumers or those reviewers who you trust/who u think suit your preferred sound preferences.
Issues like QC and derailed hypetrains will come out in the forums sooner or later. After certain IEMs stand the tests of time among reviewers and headfiers in the forums, and are still recommended after a few months, you know this set is a potential keeper.
2) You can ask others via PM on headfi for their honest impressions of an IEM you are interested in, I've done that a few times, and the community here is extremely helpful to provide their honest impressions.
3) Check out graphs/FR - they won't tell the full story for subjective areas like timbre, imaging, instrument separation etc, but you'll at least know if it will suit your preferences in areas like bass, treble brightness etc. From the get go, if you know the FR is not gonna suit you, at least you won't waste time. But if the FR suits your tastes, maybe you can go dig around for more reviews and impressions.
4) Some reviews and headfier impressions compare sets that you are interested in with those you already have, so you can tell if it's gonna a sidegrade or upgrade.
5) Buy from certain shops like amazon with a return policy, in case the IEM is not your cup of tea, you can still return it.
6) Buy second hand gear, at least you ain't making a big loss should it not suit you.
7) Audition at local shops if you can. This is pretty difficult for CHIFI admittedly.
8) Attend CAMJAMs if you can.
Though for option 7 +8, the caveat is that you can't unhear stuff that you have heard LOL. After that the market has been spoilt and the only way is up up up and deeper down the rabbithole.