Both boats are fun and durable. The weight issue with Hobie 18's is minimal. The change came in 1984, I don't remember the difference but it was minimal. Probably less than 10lbs difference. I believe the 5.8 weights is less by a greater margin than any of the Hobie 18's but I am not sure. I would stick with what you have for the following reasons

You already own it
You know what you have
It doesn't need any work
It will fufill your wants/needs that you listed.

I wouldn't switch because of the following

You have to buy it and sell the one you have
You don't know what surprises are awaiting you with the boat
You said it needed some work

Please note that while I sail a Hobie 18 on steriods, statement would have been the same if the boats were reversed. Point is, go have some fun, the difference in the boats is minimal for what you are wanting to do, but it sounds like one of them would require some money and time to bring up to snuff.