I was totally dissapointed with the FFIII-soundtrack, too. I remember the time when I just bought the soundtrack for the NES-version and then the remake was announced and I thought "damn I should have waited - they'll probably make a kickass remake-soundtrack!" - but that was probably too much to ask for... either way I'm very happy with the NES-OSV.
As for FFIV... well I prefer the SNES-version as well, but I think they did a much better job there than on FFIII - possible because the SNES already had some pretty good sound and samples and so they had a reference unlike FFIII - one problem I ahd with this was not only the synth quality but also the choice of instruments in way too many tracks. Besides that the FFIV-soundtrack for the remake is superior to the release for the SNES-one anyway, beeing two discs and giving all the tracks a more appropiate playtime. Just my thoughts about that.