I feel like G4 is the first generation with a fanbase not rooted in original G1 love.
G3 ponies are coming into their own as collector's items, because the little girls who played with them are now in their late teens to mid-20s and probably have nostalgia for their childhood toys. They had a big following among collectors when they first came out just because they were cuter than G2s and everyone was excited about new ponies coming out.
IDK about G2s. I have never liked them. I have no childhood / sentimentality attached with them and don't think they're particularly cute - never got into them as a collector. I have a few I've picked up at thrift stores just because they're ponies.