Has anyone been to this event in the past, is it worth paying the £8 entrance fee? (seems a bit steep to me when there'll be 4 of us possibly going)

never been but there is a £2 reduction if you buy in advance,
http://78.110.174.12/~oxtons/index.php?option=com_content&task=view&id=20&Itemid=36

Elizabeth, this event is always well supported. There are about 20 gardens, you can find much more on the web about it.
Maybe not so good if it rains.

Depends on your interests, if your into plants & flowers there are some great finds, some little gems of 'Secret' gardens, some(couple) you will find yourself asking 'why' did you open this to the public...but on the whole a good day out..it will take all day to do it justice. Lots of stalls & things for the kids, food etc. plant sales..Bring a brolly if it rains don't let that put you off.
Previous years, St. Saviours tower open to the public, buses from the transport museum giving rides about the village. Visit the Arno gardens to see the work being done there on the long border by the 'friends'.
Still time to get your £6.00 tickets & all under 18's go free.

Always a great day in my opinion, I think there are more than 20 gardens but I may be wrong. It's a lovely days walking around places you wouldn't normally see.

Definitely worth it, I'd say. It's a well-run, delightful community event, with stalls, refreshments, Morris dancers etc and residents go to a lot of trouble to make their gardens worth admiring. There's a real party atmosphere - especially if the sun shines! Funds raised go to local charities, too, so it's in a good cause. Some of Tam O'Shanter Urban Farm's picnic tables with games on were bought with funds from this event.

I've been when it used to be free, it was OK, but I wouldn't go if I had to pay £8, or even £6 each though.

Its an Excellent day out Gardens are lovely and at £6 each a cheap day out.They support local charities too.Take your own Picnic And sit in The Arno if its a nice day/