Unless you have a 12+:1 comp ratio you will see no useful gains IMHO. Ethanol is cheaper (a bit) however you use a LOT more than regular fuel since it has a lower energy density but very different burn characteristics. I ran E50 on my Subaru which had map switching and it was still inconvenient. If running a mix, then you will need to ensure you mix is consistent. Cars that have JB4 available for them don't have this issue as you can do a flex fuel install to monitor ethanol %...
To do this on a 325i, you will need a big investment to ensure your whole fuel system can handle eth (or else your car will smell like it all the time as it leaks and eats away at bits of your fuel system), bigger injectors, totally different map (95 and eth require completely different ignition timing and fueling maps) - so you will either have to have backup all the time in the car or have a map switching system which is also $$$. Storing ethanol is an issue as the stuff evaporates on one hand and expands/contracts DRAMATICALLY especially in these transition months between seasons when stored in sealed containers. Go to a race day and watch the guys handling their fuel mixes to see what I mean. By-laws only permit 220L to be stored in a home (some places allow double that) and you must have signage and venting in your garage (I had this at home but of course you can choose to ignore this and if your house burns down insurance will repudiate your claim :crazylaugh

. You need an account with TAG solvents and they deliver to your house (they did to mine anyway) and you will need a pump system (I built one from some fuel line and a 12v pump from Midas), since siphoning only goes so far and then You will still have tiny gains (if any) and a lot of headaches.
TL;DR: Don't do it and follow the advice of others.