Starter sets worth it?

I was looking for layout ideas in my other thread, when an idea occured to me. I'm wondering if a good, reasonably inexpensive way to get started would be to put a pair of starter sets in my "L" shaped area. I could fit one around the tree and one in the base of the "L". I'm assuming that there wouldn't be enough power in the starter sets to get much bigger, but I could probably add a few straight sections to each to make them a little bigger.

I'm thinking that this might be a good place to start, with some expansion options later. Besides, that would give each of the twin boys their own train. But my question is whether it is worth it. Are the starter sets reliable enough to last a year or two, while allowing for slow replacement of cars and parts, or will they just give out after a month or two of use? It would certainly be cheaper than building the whole thing from scratch, at least to start.

Opinions?

Thanks!
Timothy