Keep it mint.They arent making any more original series 70's and these are sought after by collectors,and kept in its original condition,its value will only go up.I have to disagree with the idea that customising a pistol increases its value,I dont think you will ever sell a customised gun and recoup your money put into customising it(unless its something like a swenson etc).Plus your ideas of custom features may not agree with others.I have seen quite a few customised 1911s on the EE sitting there for an awful long time
There are lots of factory guns out there now with all the custom features that you are probably looking for and quite frankly,the guns made today are superior than the older guns when it comes to fitting ,accuracy etc.