Keep in mind that the Hobie 20 was designed as a one-design class racer. The idea is that all the boats are similarly equipped and the ability of the crew determines the outcome of class events. Even if you don't think you are interested in class racing at this point, keep your options open by buying only class legal equipment, such as Hobie produced (or produced by their authorized subcontractor) sails and trampolines. As far as resale is concerned, a boat that is compliant with class rules will appeal to more potential buyers, and thus demand a higher price, than a non-compliant boat. Class rules are posted on the Hobie Class Association web site.
I refurbished a 1997 H20 in 2008 and have had a blast with it. I bought a new factory trampoline and in 2010, I bought a new set of Hobie sails. I can't say enough good things about them. Some aftermarket vendors will offer sails and trampolines at lower prices, but based on what I've seen, especially with trampolines, you'll get what you pay for. Here's a photo of my boat with new Hobie sails (custom order sail color and I kept the original sail number). Any Hobie dealer can order new sails for you.
Let us know where you are located and maybe we can hook you up with some local H20 sailors in your area. You'll learn a ton by having a crafty old veteran look over your boat.