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have been used for purposes other than intended

have started to become more commonplace

I think the text is referring to everywhere becoming the same

the use of this verb is a little odd here but it is clearly negative, describing about how these areas are suffering. Given the surrounding text it seems they are being 'crowded out' and are losing their 'raison d'être'. I wonder if my suggestion conveys this.

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Note added at 45 mins (2008-10-21 15:02:09 GMT)
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can't resist my embroidery! here is an interesting text about rural areas 'sliding into a decline' which seems very much what your text is hinting at although perhaps a bit strong for 'banalisarse':

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RLG 98/2a: About values, opportunism and oblivion
Advice on governing the rural area - March 1998
Reason for the advice: creeping decline


There is neither a crisis nor an acute problem, but there is a creeping decline which must promptly be averted to avoid great and permanent reduction of values. The rural area is dependent on these values for its own significance and for its importance as the functional counterpoint of the city. An important element is the open space. This, however, should not be confused with emptiness: the rural area is not empty, but has slid into oblivion, and is vulnerable. There is, therefore, much to be governed whereby the quality of the government is of great importance, too.