Aerostar problems

I have a 1997 Ford Aerostar, V6 engine with 125,000 miles. I would like advice on two areas. Firstly, I took it in to a garage because I knew I had a coolent leak. Turns out that I have a cracked head gasket. If I decide to keep the car, would it make more sense to have the engine replaced rather than fixed? I have seen a website that offers rebuilt engines with 5year/100,000 mile warrantees for about the same cost that my mechanic quoted for repairs using a machine shop.

Second question. My mechanic reported my odometer as not working and my car shifting badly making him suspect transmission problems. However, neither of these problems existed before I took it in, and also the check engine light is on when it wasn't before. I now realize that the night before I took it in, my husband tried to replace an interior light under the dash on the driver's side. The bulb had come out, but when he tried to put it back in something popped and the bulb broke. I suspect a fuse blew, which has made the LCD odometer display disappear and possibly illuminated the check engine light. Is it possible that there is a connection with the rough shifting also, or is this just a bizarre coincidence?