I never collect transformers just to earn a profit later; I find that notion ridiculous. I buy transformers because I like the mold/figure/character. I only buy transformers with a super realistic alt mode (or the occasional minicon for desk fodder). Alt wheeljack, tracks, ravage (kitty), dead end, hound, swindle, MP Starscream, and the classics predacon minicon team are the only TFs I currently own and plan to own for a while (unless Megatron gets an earth mode in the movie and a toy of it is made that looks nice). When it comes down to it...I suppose I buy TFs that dont looks like they'd be transformers.
I liked them as a kid but then stopped buying or even looking at them for a while, then BW came out and I had to get everyone for some reason. Been the same ever since(except for repaints, unless its a good one). As for value, the only ones that stay undisplayed in a pose and MISB are the ones I don't have room to open yet
Several reasons for me collecting... Nostalgia... pastime... Transforming them for fun...like a puzzle (as mentioned previously)... Decor for the hobby room... I'm also a sucker for the nice packaging in some lines... And lastly...if I do grow cold to TF's...I can always sell them...the hobby isn't a total money pit...which is a good thing...
I just collect for the fun of it.... well, maybe when I get to be a grandma, I could probably give them all to the grandkids, or sell them if they don't want them.
I collect because number one its fun, second I just love the toys and the characthers, I grew up with them, in fact its probably the one constant I've had in life, its kind of neat to have something you've liked for so long that still gives you enjoyment and I'm sure part of it is nostalgia, a number of factors I guess.
Because there isn't anything else in the world that can bring as much joy as the smell of a new toy. It brings back the nostalgia of RID and brings that same happiness I had when I was a kid.