Just to agree -- a nice vase and the signature looks 100% genuine. The price you paid was a moderate bargain, in my opinion, not a massive bargain. Remember Azurene was made in huge quantities, though Gold Azurene was less common since it cost significantly more to make at the time. Possibly buyers didn't notice it was Gold Azurene and passed it over. It is not always obvious from eBay pictures. If it was sold in the UK then I missed it too!
A signature boosts the value a lot; triple an unsigned piece is typical.
I wouldn't agree with Sue that prices for IOW Studio Glass has waned or gone off the boil recently. I was speaking to the leading dealer and most expert person I know about IOW glass a couple of weeks ago (here's looking at you Ron) who made an analysis of sale prices and found that the average increase has been 11% annually for the last seven years. That correlated with my gut feeling of a 50% increase over that time frame. Of course it varies, depending on the design, how common it is, etc. The rarer bits are rocketing in price in my experience, while more common pieces are not so buoyant, as expected.
Anton