I don't think TOMS are 'too' expensive. They are absolutely going to cost you more than the clearance rack at Target (my other favorite place to buy shoes), but considering the mission and cause you're supporting, you really are paying for more than simply a pair of shoes.
As for whether or not they wear out - I bought my first pair of TOMS my freshman year in college - almost 7 years ago - and I still wear them. They have faded a little bit colorwise (I got the artist kind so that paint has worn off some, as would be expected), but they're still in awesome shape, the sole is still attached, and there's no holes or anything :)
I see TOMS as an investment. Pricey, but in my opinion, absolutely worth the money you pay! :)