Use the checklist on buying from the documents center.
I cannot speak from Casita
experience, but I will speak from experience in our purchase of our 1979 Burro
and 1986 Uhaul
Good news: You feel no guilt making it your own. If you don't like the colors, change it. If you want to tear things out and change it, no guilt felt due to age.
You can make it your own unique trailer done as you wish.
Fiberglass trailers last forever. I have heard of trailers being buried in dirt up to the fiberglass, and they were revived to be used. I have heard of them crushed from trees falling on them, and they were salvaged. One member here cut his fiberglass trailer in parts, used a welded frame that added additional length to his trailer, and is almost done putting it back together (Amazing!).
Bad news: The bad news really revolves around three things: how the previous owners kept it, how handy you both are, and how much time you have towards applying that handiness.
Almost any fiberglass trailer, regardless of the condition, can be revived if you have the skills and time to apply it. Broken fiberglass can be fixed, supports can be replaced, wiring can be redone.
So find the buyer's checklist, weigh your time and talents, and go look at it.
PS: Be sure NOT to include Blue Book values in your decision! I cannot tell you how many people who post here asking for help in the purchase who assume that Blue Book value or their assumed value of a vintage fiberglass trailer cause them to lose the purchase.
We bought our Uhaul
VT from someone who was doing just that, questioning the purchase of the VT. He made the mistake of asking about it and giving the link to the ebay ad. I followed the link, and ten minutes later, we bought the camper from the lister who provide a buy-it-now. (Do I feel guilty? No. In the world of fiberglass campers, you snooze, you loose! Keep that in mind as you are thinking of a purchase.) Yes, it has cost us around 2000 dollars in additional fixes, but it has taken us places we never would have gone without it. I can safely say that it has changed our lives.