OP, I know how it feels when you want to be spontaneous, and you feel ADR's will restrict you. I go to Disney frequently, and seldom make ADR's far in advance. However, I go solo most of the time, and I also go during slower seasons. I also don't mind eating CS if I can't get in a TS restaurant.
In your case, with 8 people, I think you have a few options.
If you intend to eat TS in the parks or at nearby resorts, I would at least call the day before and get an ADR set up. I'm not saying you need to book 90 days out, because as you said, you don't know what you want to do at that point. But I wouldn't go into the park with a party that size and try to wing it. Many of the restaurants have very limited numbers of tables that hold more than four people - so at the very least you risk not being able to sit together if you don't plan ahead. Character meals are an ADR must - don't try to walk in unless you're prepared to be disappointed.
Another option, mentioned by a pp, is to dine off property. On days when the parks close a little earlier, this could be a really viable option for you. There are dozens of decent quality restaurants just outside Disney that won't cost nearly as much as eating TS in the parks. This may not work for every night, but you might do this a few times.
You could also just snack your way through the day and plan to eat back at your villa. This would save you time, money, and aggravation, and you could be as spontaneous as you please. I know when I do day trips to the park, I eat a substantial breakfast at home, snack at the park during the day, and then have my other meal when I get back home.
Of course, there is always the option of just dining CS. It's not so bad as it used to be - there's a lot more selection than just hot dogs and hamburgers. Disney has even started a new CS only dining plan. I was on a strict budget Christmas trip last December, and ate only CS for five days. I didn't feel like I missed out on anything, and I could be as spontaneous as I liked.
So go to Disney, with or without your ADR's and have a great time!