42 Grams should be a really interesting, fun experience with some highly creative food. The only caution would be if your wife wants an intimate experience; 42 Grams has no tables for two; just a communal table and a chef's counter. At both of these you'd be seated with a group of people and be served your courses simultaneous. So long as your wife is not expecting a more intimate celebration, no big deal, but something to consider if she would find a communal dining experience acceptable for her birthday dinner.
Another restaurant similar to 42 Grams and El Ideas in terms of providing a lengthy tasting menu of highly creative, unique cuisine would be Elizabeth Restaurant. While Elizabeth used to be communal tables, they now are set up like a more traditional restaurant where each party is seated at their own table and dined at their own pace. It is set up somewhat similar to El Ideas with an open kitchen and some interaction with the chefs. The food has a farm-to-table emphasis and Chef Regan plays a role in obtaining much of the food herself via foraging, growing and occasionally hunting and fishing.
Other restaurants I love that are in the price range of 42 Grams/Topolobampo/Elizabeth, that likely have availability and that I think would be good for a special occasion would be Senza (modern American cuisine; choice of a nine course tasting menu of five course prix fixe - fine dining quality food but neighborhood bistro ambiance and extremely friendly staff) or Boka (Contemporary American; a la carte menu - though tasting menus sometimes accommodated upon request; simply amazing food, very nice decor and space and wonderful staff). Boka is even a bit less expensive than the other venues.
Topolobampo would not be my choice for a special occasion. I love the cuisine but find the ambiance very touristy and tables are uncomfortably close together; service I also have found to generally be quite poor. Awesome food, but I just wish the overall experience was better.
Twitter: @Goof_2