Though I can't tell you if it's worth it or not, I can point a few things out I've found in my project with my 170.
1) a little problem tends to be just the surface of a big problem, so the weeping problem could have caused issues further in the engine if someone hasn't been careful.
2)The 470 is also based off of a Ford engine, so that might be a consideration for repair parts and farmilarity with Ford engines.
3) I have a stringer OMC drive, and parts are near impossible to find, so plan pick something that has many readily available parts (if its a outboard, I'm sure that won't be as big an issue for you).
4)Bust Out Another Thousand. I've heard this before and didn't really realize it until I started into my project, Boats won't nickle and dime you to death, they'll $50 and $100 you to death

Like you I'm a driveway mechanic and honestly I've found boat a little simpler to work on than cars, but with that being said, it's still a challenge. I took the plunge with a much much bigger project and thought I knew what I was getting into. I didn't, but it's still not beyond my skill sets.
If it fits your budgets, don't mind not getting it out onto the water until later and your confident that you're comfortable to tackle bigger issues than you can see, I'd say go for it. But just like cars, you can't tell what's going on in the engine until you crack it open.
Oh and I don't regret my project for a second, the challenges it's provided me and fun it's been tinkering on it every weekend. If it's even half as fun on the water, I'll be a boat owner for life.