Regarding COMC:
COMC is its own micro-economy. The stuff that happens there do not necessarily correlate 1:1 with eBay etc. The good news is that it serves as a focal point for collectors to buy cards and often times cheaper than in some other areas for certain items. With Metal (and ePack in general) , there is huge emphasis on achievements, rendering other cards as "useless" creating a false economy where people race to the bottom to dump their cards. This is where collectors can benefit. ePack is not going anywhere and if anything is gathering more and more steam with each passing release.
As for Metal, we've reached metal fatigue. A LOT of products have had metal clones across Metal Champions, Skybox, Marvel Metal products etc. That being said, I suspect the lull in popularity to be short lived. This is an opportunity to get certain issues cheaper than in the future. Having said that, Jimmy Vesey PMGs ain't gonna ever get to levels where you can bank on it so keep that in mind.
I will pick up the key ones I want when the price is right. I will hold them as I like the look of them.. I prefer the older ones as Jeremy mentioned. Those have nostalgia in mind.
As a cute side note, the definition of metal fatigue in metallurgy is this..
"metal fatigue, weakened condition induced in metal parts of machines, vehicles, or structures by repeated stresses or loadings, ultimately resulting in fracture under a stress much weaker than that necessary to cause fracture in a single application".
I'd love to see a side insert set with this in mind haha..