I just had a luthier do some fret redressing on my old Sheraton II (not used it in a long time). When he saw it he was amazed, said it was very rare to see one of the 80's ones and that it was worth a fair bit as it was vintage (to me the 80s is NOT vintage, cos that means I am!).

I personally don't believe him but he was adamant about it. Its the natural Epiphone Sheraton II from 86-88. Not sure about the exact year as I bought it second hand in the first quarter of 88. The headstock inlay says Epiphone by Gibson which apparently they stopped doing in 89. Its had the frets redressed and a new bone nut fitted but apart from that and a few small minor scratches and a little ding on the side its mint.

The quality of the 80s Sheratons is, IMHO, better than the modern ones, although not by much.They were about £350 in the 80s, I'm guessing it would be worth about £250 to £300 now. Am I wrong, what do you reckon?
I have a 1987 "Epihone by Gibson" Sheraton and I don't care how much it's worth. It isn't going anywhere. It's a keeper!

Yes, your Epi in good condition will command a higher price, and for good reason. It's a solid instrument. Anyone who is in the know will want it. I'd recommend you continue to keep it and play it! That you've kept it this long only adds to its value. People love to buy things kept in good condition a long time by a caring owner.