Value is VERY dependant on which model as there were SEVERAL 4HP OMC's built. Is it a base model kicker, or a deluxe model is the big question though. Some 4HP kickers were locked into forward all the time, and turned all the way around to give you reverse. The deluxe model has forward, nuetral, and reverse, and is like a regular tiller outboard. As to how fast, I had a 4.5HP(in the late 70's to early 80's, OMC called the deluxe model the 4.5HP instead of 4HP) that took a 12 foot semi v bottom aluminum jon boat, and picked it up and ran on plane with it(probably close to 18 MPH if I had to guess). It even had enough gusto to it to get the boat up on plane with 2 people in it. That same outboard we used for MANY years on a 16 foot wide jon boat. Sucker SIPPED fuel, was slow as all get out, but always got us there and back on a few gallons of gas. It pushed the 16 footer up close to hull speed which was about 8MPH or so. Every boat has a hull speed which is the speed it can go before it gets on plane. Hull speed takes very little HP to reach, but once you approach it, it is where you need so much more HP to overcome that speed. If it is a base model locked in gear model, they only bring a few hundred bucks, but the deluxe models can bring $700-1000 depending on how nice they are.