Bianca was declawed when she was about 6 months old and had no negative reaction towards it at all. She acted as though nothing happened. I'm ashamed to admit though that all 4 of her paws were declawed as was my second cat's (he was done when he was about 4 months). My third cat, however, is not declawed, but I have soft paws on her.
I don't intend on declawing again if I ever do get another cat in the future (years and years down the road, lol) but neither of the cats I had declawed showed any negative reactions. Just thought I should throw that out there because I know how horrible it is to declaw cats.
I allow the cats to go on all my furniture, the counters and etc. Bianca does go up onto the dresser and bar table (which are pretty high) every so often, but the other two usually follow her anyway and chase her until they lose interest or are distracted by the other one.
Age wise - Bianca is 4 (she'll be 5 in Dec), Cash is about 1 year 2 months (adopted Dec 2010), Annica is 1 year 1 month (adopted Apr 2011). Cash was a kitten when I introduced them and she had a negative reaction, but after I had him fixed she calmed down. I kept Cash in a specific area on his own for a few days, allowing her to get used to his scent.
With Annica I introduced them to see how they reacted and they were fine until Annica freaked out and then I moved her to a room on her own while leaving the carrier out so the other two could sniff it. Cash and Annica became quick friends and get along perfectly.
I noticed after I got Cash she started missing the liter box, I assumed that was all it was, but now I wonder if maybe she was spraying to mark her territory. I didn't think about that before you mentioned making the situation more tolerable.
I live in an apartment though, so I'm thinking the small space might just not provide enough privacy for her. I'm curious as to what I can do to make it more tolerable for her as I really do want to keep her, she's been my baby four so long it just feels wrong to even consider giving her up.
The only other thing I want to add is that the Wisconsin Humane Society is a non-kill shelter and I volunteer there - they are a GREAT facility and I've seen 12 & 15 year old cats be adopted out there no problem. I wouldn't give her to them if I didn't know first hand that they would find her a wonderful home.
I would still like to know what I can do to help and I want to at least try before I make such a huge decision. I don't have a lot of money, so I'm not sure I will be able to buy cat towers and whatnot, though I do have a few cat city ones that Bianca doesn't seem to really care for.