purchase advise: used Jayco x213 or new Jayco x213?

I would go for the new one for several reasons.
1. You can afford either.

2. New gives you more room to expand as family grows.

3. Tanks are larger which will give you more flexibility during dry camping which you say you prefer.

4. You will have a warranty with the new one.

5. Old one was stored outside so there could well be hidden leaks from lack of roof maintainence - even if you can't see it from the inside.

6. There is nothing like that "new trailer" feeling! :)
Barney