It's a very nice Festival series guitar, Will, and from the serial number I'd say you're right about the production period...but the serial number starts with "90" so that suggests that it is a 1990 model.
The Festival series is a unique beast...played unplugged they sound very "thin", not like a full size guitar would sound...but when they are played "juiced" (through an amp or a PA system) they really shine.
I must say yours is the most attractive Festival series guitar I've seen. The use of the gold on the tuners and the "...burst" (the paint job on the soundboard of the guitar) make it a real standout visually. Do you have an amp? You'll need it if you want to hear it at its very best.
I will continue to search the archives for more information for you, but you've posted your question in the right forums.
Speaking of which, the forum seems to be the "red headed step child" of the administration of Washburn. I can imagine why...their "Facebook" presence would undoubtedly be more active (Facebook seems to be taking over the net at times), so the forum isn't getting monitored and many of us cannot post on the forum for various reasons. For me I must be on a PC to get my posts displayed, if I try to use my iPhone the forum refuses the post and says if I get that message again I should contact an administrator...which I have done numerous times and have never even gotten a "...go to hell" response, much less seen the issue resolved.
Many of us who have been here for a long time see this as the end of the forum. Do you Facebook? If you do I'd suggest you try the Washburn Facebook page...or do they call it a wall? I don't Facebook, so I don't know what kind of stuff is on their "wall".
Hope you'll continue to post. That is an absolutely gorgeous guitar! I'd suggest you have it inspected by a good shop tech or a luthier...if you haven't played it, you might find that there are unexpected buzzes and snap, crackle and pops from the electronics. They get corroded and gummed up and then the guitar sounds like crap. It's nice to see you like it. I've had many Washburns and surprisingly my WD32SW (an all solid wood guitar, supposedly the best construction available) is the most difficult to play guitar I've ever owned. Perhaps consistency was one of Washburn's challenges?
Hoping I can find more info for you, but you might run a search for your model number and be surprised how many (or...how few) there are out there. The search function is directly to the right of "Home" on the grey bar at the top. I'd search for "Washburn 1990 Monterey Artist"
As for a valuation, well, our forum member Tony Raven has provided them at times, but he is very vocal about the amount of time it takes to do one of his searches (and his most often used source of information, the "blue book", seems to be on the way out as the world switches from pencil and paper to digital/internet) and how much his time is worth. I'd suppose he's right about that...but he's the best historian we have for recent Washburns (Ship of Fools is very knowledgable, too, but he specializes in the older parlor guitars, so he may not know about Festival.
As time permits I'll continue to search for information for you, but tomorrow I fly out from Kansas for a week moving furniture back from the Houston, TX area, so I won't be on the forum much since I can only post from my iPhone and the Washburn forum says I can't.
Later!
Dugly