The 10x12 home wall expansion is brand new, and at least when I checked a week or two ago had a grand total of 18 additional problems over the 7x10 homewall.
Another thing to consider about the Homewall expansions (and I have not used one so it's just my guess/judgement) is since it's simply an expansion of the homewall, the problems are likely going to be hard, since it involves climbing through the original 7x10 but with just more moves.
I would personally really prefer to get a 12x12 original set up since the number of problems is roughly 8,000 vs 1,000 on the home wall, and the holds are a bit more friendly on the original set up, so a bit better for power endurance and less tweaky on the fingers.
However, I think the 12x12 holds are ~$10k alone, plus the cost of a board/frame it really does become a lot more expensive than the home wall.
I also second Prav's comment, the lack of a kickboard makes some problems really hard or impossible so you might want to make sure you're leaving room for one, or realize many of the problems have hands on the 3rd and 4th row which makes them really hard to start so your available problem set might be smaller than you think.
If anyone here is selling a 12x12 kilter board I'm definitely in the market :) Nevada/Arizona/Ca area.