I think you've done very well in terms of it holding its value. There are two factors here. The first is that Murano/Venice can be the most expensive place to buy Murano pieces. The second is that Murano prices have gone down in value in last few years. In other words, you have two factors going against you, and yet I think the price you paid was a very reasonable price for a very nice piece of glass. For me, it would be a cherished memory of a visit to a wonderful place, as, I suspect, it is for you. Personally, I wouldn't be concerned about resale value, but I would be happy knowing that I bought a wonderful thing at a reasonable price.
I hope this helps.