Well I was 12, and had two, so the old ones have kitschy vintage value (i still have one going), but the new ones are better imho, even if the other people in my lectures at uni think that I'm unbearably odd when I fiddle with my tamagotchis during class. Apparantly RNs don't play with childish toys - it's 'unprofessional' lol.
I was in high school when tamagotchis first came out (I'll be 23 this year), and I have one of the original ones because I figured of one came around that I really liked the colors of, i'd go ahead and get it. I do prefer the new ones, though, as they have better graphics, sounds, and all the new features. My boyfriend thinks i went overboard having the *modest* collection I have (see my sig), but after all, he's the one who encouraged me to get back into it since I missed my dear departed pets so much and just can't have any animals in my life right now (moving, apartments, etc etc).
As long as you get all your adult responsibilities done, who says you can't play with toys?
When I was younger and Tamagotchis were really popular, I didn't own one myself (my first virtual pet was a Dinky Dino xD), but I played with a friend of mine's... I wasn't very compelled to by one of my own. But now that I've bought a new one, I really like it. I can't wait for the v2 Connections come out this summer.
I like the new ones. The new one I have now is the only one I've ever had my brothers had the older ones but the new ones look good with a nice egg shape. I've never used one of the older ones.