Sorry Adrian, but I'd suggest you have a look at the historic RW events pages - there are bound to be forums re the race, which would, I'm sure, give you more details re the event and what RW forumites thought of the race. I have a feeling that the race 1st started in the mid 2000's (2004?) and I'm fairly sure the last one was in 2010. Anglesey now has a few other races now including the brutal Coastal marathon and the Ring of Fire (mainly) off road events (as well as the half previously mentioned)
Having liaised with someone from the local club, it was organised by Mentor Mon. I understand that it cost quite a lot to put on the event (the hire of the show ground and Colin Jackson's appearance fee [£5k!?] being a fair share I'm sure). I do recall thinking the race to be an absolute bargain, but at the same time I thought it deserved to be supported by more runners - I think the year I did it it was the British Masters marathon champs and I thought the number of runners who took part was a bit disappointing. I guess in times of the recession and council cutbacks this event (which must have been loss making) was one of the 1st to be culled!?
The Anglesey event also had a 10k and half event on the day (re the half, I seem to recall the entrants were bussed out to the half way point of the full course). I remember it being relatively cheap to enter and getting a nice tech t-shirt plus home made stew afterwards. The organisation the year I did it (2008) was excellent. I think the event was under the umbrella of the Anglesey Festival of Running
Agree re the Anglesey Marathon - a real toughie - used to be well organised and had Colin Jackson each year at the presentation. I understand it stopped due to money issues
Also in North Wales, there was the Great Orme challenge race (run by the local branch of the British Lions) - it started off as a 5k (finishing at the top of the Great Orme - must have been one of the toughest road 5k's in the UK), then latterly became a 15k - last held I think in 2012. The Llandudno 10 miler was a very popular race which came back on the race calendar about 3 years ago, but I understand that issues with traffic management and costs meant it wasn't held in 2013.