If it is 160 across the board, there are definite issues. The minimum you should ever be looking at is 140 psi, so there is something wrong. Could be your valves or rings but you will need to replace whatever is bad. You can be as easy as you want on it but there is something wrong that needs to be fixed and being easy will just prolong the inevitable....

Modifications don't add value to a car. If your car was stock, i'd say it would be worth about $7500 or so. The mods will take away some value and with the engine problems, you would be lucky to get $6000 for it.