Value always depends on who the buyer is and how bad they want it! It could go either way on the value if you change the engine. I personally recommend you keep the 300 4bbl. They are really strong running engines. With some mild head porting, bigger exhaust, and a performance cam, you will be surprised how good it will run. The 300 is light too since it has aluminum heads and intake. The 64 with the 300 engine is the most well balanced weight distribution of all the Buick A-body V8 cars due to that.
One thing you need to know up front--the 64 engine mounts are unique to the 64 model only and no longer available. You can pretty much guarantee yours are bad and if not broken yet, will be soon if you drive it hard. You can replace the rubber mounts on the engine with the 65-67 mounts, but you also have to change the pedestal on the frame that the mount sits on/bolts through to the 65-67 style. You will have to get the pedestals off a 65-67 parts car somewhere.
Hubcaps I have are like the ones in the picture of my car I posted. I will sell all four for $100 plus whatever the shipping is to you.
