I thought about having more than one town for a while, but I decided against it. My town is always changing and growing and I like it that way. I'm not in it to have the "perfect town". I just want a town that I can change to look how I want to.
I'm not sure if this choice is supposed to depend on money or not, but overall I don't want an extra copy. I don't think it's worth the money since I will only be using it to mess around anyway (for weeds, hybrids, items, etc) and honestly once I start cheating like that I'll probably won't like playing my actual town as much anymore.
If they were free though, I would get an extra town and see what I could do with it, but in the end it'll probably be abandoned anyway. I think we should just live with the fact that we only have one town and make the best of it, you'll eventually won't be spending as much time on your main time as you would without an extra copy.
I have three copies, two proper towns and a cycling town. I justify this because I a) work and earn my own money, dammit, and b) I've put a cumulative 500 hours into these games, and what else can give you that kind of enjoyment for less than ?100? I don't think I've played that long on all my PS3 games combined.