As justifications go for not using a particular language feature, this is pretty weak.

It's akin to never using regexes or hashes, because you might choose to swap the application to using a langauge that doesn't provide them at some unspecified point in the future.

Also, your perception of the mainenance problems are very short sighted. SPs come into their own when they are written and maintained externally to the applications that uses them. To any given application they become just another library (use DB::XYZ qw/ xyz_fetch xyz_update /;). In this respect they have the same maintenance issues as any other CPAN or in-house module, which is usually seen as a plus not a minus.

As for "permature optimization" aspect. There is a worse evil than premature optimisation. It is the assupmption that all optimisation *must* be premature.