GREAT QUESTION!!!!
i have thought this many times especially when buying G3s and trading them for G1s...
i always wonder if i will regret not collecting the G3s
so far all i can think is that kids right now dont seem to be AS interested in MLPs like we were in the 80s
so i dont think there are as many potential collecters in the future, and therefore not as much demand, a TON of supply and then not as much value.
PLUS there is no G3 cartoon on tv which to me seems to boost kids interest a LOT
and increase the warm fuzzies and nostalgia that we get when we see ANYthing related to G1
but then i thought, there will always be us 80's kids who collect G3s as well.
BUT all of those like us are adults and have been buying them MIB for a while and can afford to do so as adults.
So basically anyone who would be super into G3s in 20 years will already have them MIB or MINT from collecting them now.
phew! that was a mouthful
but thats my logic thus far