New Family Member?

We live in a neighborhood with a LOT of cats wandering around.  In fact, the other day, Paul and I sat in our living room and watched one of the neighborhood cats through the window - we were very amused.  The cat was walking down the street and came upon a car parked there.  It got curious and started investigating.  Low and behold, the drivers window was totally down.  Guess what kitty did?  She jumped up onto the ledge of the window, hung out there for a few minutes, then jumped inside.  For the next 10 minutes or so, kitty investigated the inside of the car - climbing on the backs of the seats, climbing into the windshield and the rear windshield...  I was half hoping that the owner of the car would come out and start to get in with the cat in there!  That would have been enough to keep me amused for the rest of the day, I think!!!  (remind me not to leave my car windows down if my car isn't in the garage!)

Most of these neighborhood cats belong to, or are at least fed by the people who live across the street.  I was once invited into their back yard and saw at LEAST 25 cats in and around the house.  I'm sure there were plenty more that I wasn't able to see!  They tell me they do cat rescue, but most cat rescue places try to find new homes for their cats...I don't think they do this part of it.  One of their cats, called Buttons by them and Thumbs by Paul and me (you'll understand our name if you ever meet him), comes to visit us regularly.  He's the sweetest thing ever (next to our Mia, of course!).  He'll stare in the windows and meow, waiting for me to come out and pet him.  When I get home from work and he sees my car, he'll follow me up the driveway, he'll even go nose to nose with Mia at one of the screens trying to make friends.  She used to get VERY upset and make the worst noises ever and puff up into a huge furry hairball.  Now she just lays there and stares back at him (thinking evil thoughts in his direction I'm sure).  Yesterday I sat out on the front porch with him for about 20 minutes.  He climbed into my lap and just purrrrred away, completely content.  I always feel bad when I get up to go inside because he always tries to follow me in and looks really sad when I don't let him.  He's one of those cats who THRIVES on attention, but his owners have so many cats I can't imagine they're able to give him as much as he wants.  

What I'd love to do is talk to his owners and see if we can adopt Thumbs.  I think he'd love to live with us - he'd get the attention and companionship.  I think Mia would get used to him and befriend him...eventually.  I even think he'd probably convert to an indoor cat ok.  All he ever seems to want to do is eat and be pet.  He can do these two things inside, right?  So do I ask the neighbors?  Will they be offended that I'm asking for one of their cats or will they be happy that he's going to a good home?  Also, I had to do a lot of begging to get Paul to allow Mia to move in with us.  He was an avid hater of cats.  But he absolutely ADORES her now (except when she walks across his head in the middle of the night), but I'm not sure that I'd be able to convince him to allow another cat into our home.  He'd probably be concerned about the cost of another mouth to feed, but really - cats aren't that expensive.  The most costly part of it would be the vet visit he'd have to have before moving in.  We'd need to make sure that he doesn't have anything that might get Mia sick.