Sorry to hear you've been under the weather :cry: (and just about everything else by the sound of it!).
When I had the "mustard" lump removed, it cost about £8. I know, though, that having a bit of textured Strathearn sorted, which is a much more complex glass than Mdina, cost a lot more, nearer £35-40. I think the extra came from the fact that the Strathearn was textured as well as multicoloured, while the Mdina was just a straightforward polishing down on what was thick glass to start off with.
Would you end up loosing some of the opaline effect if yours were polished?
I reckon just leave it, if you can live with it.