1. Microsoft hasn't formally announced a minimum hardware specification for Vista yet, but that's likely to happen very soon.
2. Yes, I've tried it, I'm using it now, and yes, so far it does seem pretty good. There's a way to go before launch however, and I expect a great deal of tweaking to be done before then. In general terms Vista has a great deal that's good in terms of security, stability, and eye-candy, but whether or not it's something that the average home user will want/need in the short term remains to be seen. I believe that there's a good deal of mileage to be had from Windows XP before it's finished, and strictly between you, me and the rest of the planet, I think we'll see another service pack for XP shortly after the Vista launch. That, if it's released, could contain quite a lot of what's in Vista anyway. Power users, and people like me - Microsoft calls us 'early adopters' will want Vista, simply because it's the newest, shiniest thing in the shop.
3. I recommend that you think carefully before splurging on Vista soon after launch. Everyone's hoping that by the time the beta program ends there won't be too many glitches. There will be some, there always are when a new O/S hits a few million real-world machines, but Microsoft is getting much better at developing and testing - I've been using a beta version for many months, and it's rock steady.
4. Pricing will be complex, because there will be many different Vista versions, and in answer to your question, no - Microsoft has not released an official price list yet.
I hope that helps.