If you bought that frame for £35 in the mid-'80's I reckon you did well...
I paid almost twice that for a secondhand road frame, (not Mercian) at about the same time, and I thought I
was doing well! Still got mine too, and the Cinelli criterium bars... and unlike me, you obviously put it all to it's intended use.
Also, looks like you got a classy, timeless colour-scheme into the bargain
It's strange how fashions change. I remember wanting to have the frame resprayed in a 'modern' colour scheme and have all of the relevant braze-on's fitted for the cable guides, water bottle etc. I am glad I could never afford it though now!
I did look into having the frame refinished at Mercian a couple of years ago but have come around to liking the used / patina look now. I also realised that the paint job would probably cost more than the frame is actually worth. I call it patina, every scratch tells a story (something like that anyway).
I will have to have a word with my Dad about how much we a actually paid for the frame - I remember that it was advertised for about £70 but that my Dad told us how he had bartered the seller down... That is exactly the sort of thing I tell my wife now though when I spend more than I am supposed to on upgrading my son's mountain bike... Or perhaps that is just me!