We've used it on many occasions and we'll continue to do so, but it's so hard to quantify whether or not it would be 'worth it' for someone else.
It's a pleasant environment away from the hubbub of the airport. We figure we would most likely pay inflated prices for a mediocre breakfast in the airport, so we can immediately deduct that from the £35 cost. There are both hot and cold options. You won't get a huge plate full, but there's nothing to stop you ordering more than one. I'll often have something like scrambled egg and smoked salmon on an English muffin and then one or two items from the buffet later on. You can help yourselves to cereal, juices, smoothie shots, yoghurts, pastries, bagels, croissants, etc. There is no limit to the amount of food or alcolhol you can consume. We've never noticed a reluctance to serve anyone or any kind of judgemental body language, although I'm sure they would refuse to serve anyone who was becoming drunk. When we were there with friends in April (4 adults) we got through 3 bottles of champagne - they just kept bringing them.
There's also an internet room where you can get online and DIS for a while.
We normally check in early (around 7am) so that we can get through security, do a bit of duty free shopping and then settle in to the lounge. They will announce your flight about half an hour before it's due to leave, so we often depart the lounge and, by the time we get across to the gate, walk straight on to the plane. If there are any delays, they'll keep you updated, so there's no need to leave the lounge until you absolutely have to.