We have a lovely soft play close to us, which is similar to what you describe. It's inside a park (in a pavilion), and has an enclosed outdoor area which they only set up in summer. The outdoor area has lots of climbing frames (the plastic little tykes type), rides ons and an awesome little train on a track. Indoors there is a bouncy castle, a big ballpit with soft play shapes, a couple of toy kitchens, lots more ride-ons, buckets full of toys like trucks, musical instruments etc, and a blocked off corner with soft mats for the little ones.
They charge £4.50 for the first hour, and then about another £1 per extra hour (you pay the remainder when you leave) . Under 1 year is just £1 for as long as you like. I'm happy to pay that amount for DD now (2.5 years), and it was fine when she was under 1. It felt like a big jump when she turned 1, and she was just walking but not really big enough to take advantage of all the bigger things, so I stopped going for a while. The baby area is a bit of an after-thought though. I would have been happier to pay if there had been a more pleasant area for babies (bigger area, more age-appropriate toys, not jammed in the corner).
I drive there about once a month despite there being other soft play places within walking distance, and it being inside a park with playground (we often go to the playground afterwards). The reason I go there is because it's a really pleasant, bright environment- I hate big, gloomy warehouse soft plays, and I hate noisy places (their bouncy castle is mercifully quiet). Also, if it's sunny, it's lovely for DD to be outside, and with all the rides-ons it does feel materially different to playgrounds - so the outdoor area is definitely a big draw.
One disappointment is that it's closed on weekends. I would go more often at the weekend than during the week if it was open - since 'mummy friends' are typically with their OH, so we don't go to each other's houses. I know it's probably inconvenient, but I'd strongly suggest being open weekends and holidays.
A soft play I went to once had an organised activity most days at a specific time in the morning,which I thought was fantastic. It was included in the price: if you were there at that time you could just join in if you liked. It was simple things like singing one day; craft another. It's a simple thing to provide (since it's just for half an hour at a specific time), and it's a big draw - especially in the holidays when most groups stop.
I don't usually stay for food. I'd consider it if there was something simple DD would eat, eg a cheese sandwich (for £1 or less since I'm never sure she'll eat it, and it's depressing to pay more and have it left untouched), and a sandwich or toastie for me. But I do wonder about the whole concept of not letting people bring food for the children. Another really lovely soft play cafe I've been to DOES allow you to bring sandwiches for the little ones. I have to say that I actually spend more on food there than at other places, since I can bring sandwiches for DD which I know she'll eat, so I'm more likely to stay for lunch and buy something for myself. If I can't guarantee that I can get something DD will eat, I'm much more likely just to go home and avoid that stress.
Proper homemade cake would definitely be a draw 
and proper coffee (all the coffee shop options like cappuccino and latte) is also something I'll pay coffee shop prices for.