Hello thebaron, and welcom to cruise-chat from me also.
I was in Ocho Rios for the first time just a few weeks ago. I was apprehensive because of so many things I had read; but I must tell you we really loved it. It is a beautiful, lush area with turquoise water and white sand beaches.
Yes, you have to keep your wits about you and use your common sense, as you would in any foreign country, as Penny says. The street vendors can be aggressive and intimidating; but we found a firm "no" was all it took. The passengers with all the necklaces that night were the ones that made the mistake of showing an interest in the trinkets. Don't look interested unless you intend to buy.
There is no need for a ship excursion to do the Falls and shopping. Again, as Penny says, just make sure the cab is licensed; use the ones with the red license plates and agree on the fare first.
We loved Ocho Rios; I'm sure you will too.