A quick grep shows that ALSA_PCM_PLUGINS is not used anywhere. Please consider dropping it.
Sorry to have missed that aspect: *alsa-lib-1.0.25 (26 Jan 2012) 26 Jan 2012; Tony Vroon <chainsaw@gentoo.org> +files/1.0.25-extraneous-cflags.diff, -alsa-lib-1.0.23.ebuild, +alsa-lib-1.0.25.ebuild: Version bump. Do a full eautoreconf to avoid failures with et_EE locale, closes bug #361053 by Mart "leio" Raudsepp. Remove extraneous CFLAGS, closes bug #378653 by Agostino "ago" Sarubbo. Prevent build failures in the library and beyond by not allowing individual plugin control, closes bug #379925 by Myckel Habets. Removed old ebuild. I can confirm that no ALSA packages use this. If you are willing & able to remove the USE_EXPAND definition, please proceed.
Dropped from all profiles.