Some of the older tamas are starting to act st rangely already.
I am in a group where we do group hatches of certain things at certain times of the year and some of us have had problems with some of our stuff already. The Tamagotchis can go bad after a few years especially if you leave the batteries in.
I take the batteries out of everything I store in the safe but I often forget to take the batteries out of the other ones. One of these days, I will have to go through my bins and just start taking batteries out!
So people have to think ahead when they do the long term storage thing.
As far as collectability goes, it's often the most common ones will turn out to be the most desireable ones in the future.
It's like collecting cars! It's the ones you saw 25+ years ago that you will want again. Not usually the uncomon ones.
But I suppose that when people decide to collect, they will go for the more unusual ones like Yasashii *yawn..* or Devil *good luck*
The rares have problems all their own.
Yasashii is not the greatest play wise and the characters are not cute at all. Then the Devils had soft screws so it's hard to find one in perfect condition. The 2 Devils I play with both have to have their backs taped down because I had to drill out the screws. That is a common problem for the Devils.
When you collect, you will hear about the quirks these things can have and you will just have to take your chances on what you get.
So weather or not these will keep their value, increase or decrease in value is a mystery.
Never collect because you think there could be a market for them in the future. Collect because you love what you collect