If you buy it, and spend time on it, it's only your time and maybe a bit of parts and consumables like fluids and filters. Hard to go to wrong as long as you're having fun. If you get to the end of it and it doesn't go, you've only got $1,000 and some time in it, and probably learned something. I reckon Kubotas are generally pretty robust, if it was running 5 years ago and was stored reasonably well (no water down the exhaust for example) there's a reasonable chance it'll run again.
If I had the time I'd give it a go. Then it's just down to price, and that really comes down to how much you can afford to lose. If you can pay $1,000 and it turns out it never runs and that's OK, then do it. If that would break a friendship because you'd be upset, then don't go there.
I also think some of these tractors are worth a bit if you part them out. If you can afford to have it lying around and sell of pieces bit by bit, you'd potentially get your money back. The loader on its own could be worth $1,000 if it were working.