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Smaller wheels means lower unsprung weight and inertia (per axle) and (with lower axle loads) gives better ride quality. As you suggest (and I hinted at) the wear on the brakes (and tyres) is greater, though being smaller they are cheaper (apart from labour). Wear of the rotating parts shouldn't be a problem (I'm pondering about drive-axle ratios . . . ).
The brakes on the VAL suffered from fade, especially when used for Continental Coaches operating in mountainous regions. Use for service buses (except, perhaps in Sheffield) shouldn't cause problems - though some may have better-informed information than mine.
Perhaps some operators running small-wheeled trailers have some useful input?
The VAL used conventional semi-elliptical metal leaf springs, whereas modern designs would undoubtedly use air suspension (this is almost universal for kneeling buses). Again, air suspension gives improved ride quality, so the benefits would be compounded (and further reduce mechanical wear - assuming sensible sizing of components).
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