of course i have thought about it and know all the differences in specs. however i already own an S3 that i like very much and this is a DIY board on a site dedicated to squeezing the most out of what we already have.
have you looked at prices of S5s lately? they've gone up! cost is always a factor which is why we have CHDK and 1000 other hacks and mods. otherwise we can already get cameras that save RAW.
do you have an S5? if so i have some questions for you
1) do you think the 8mp 1/2.33 sensor does any better than the 6mp 1/2.33 sensor on the S3?
2) can you measure around the area of the pop-up flash? specifically the width of the bottom plate.
You would be better to upgrade & buy a secondhand S5IS they are a nice camera :-)