The 3DS has a lot of games you can't play anywhere else, and there's a lot of fun games on the system.
You don't have a 3DS yet?
Now again, we used it only to play games (games that weren't even that good to begin with). We sometimes use it to use Google or YouTube, but my little brother will get a phone this Christmas, and at that time every member of the family will have their own phone. Which would make an iPad not as worth it and more expensive.It more depends on whether or not it's suitable replacement to the iPad. You referred to it as "our iPad", does this mean other members of your family use it? If so, then they may do things besides playing games on it, meaning they won't have a suitable replacement if you buy a 3DS. If it's just you using it to play games then buy a 3DS.
The 3DS is worth buying, it has a vast library of games spanning two generations (DS and 3DS) and also has a Virtual Console, it's just a question of whether or not it's a suitable replacement for your iPad.
No, you should still definitely get one.No, there's no point in buying it when you have a far superior console that isn't going to die soon and has good games. Unless you don't have DS, then buy it because then you can play DS games on there (which are actually good).