I believe that the important thing is setting a realistic goal for the number of interviews. In this specialty, for an AMG without failures/red flags who interviews reasonably well, fifty interviews would just be a lot of unnecessary expense. This is where specialty advisers can really help an applicant target the appropriate programs to apply to in the first place. I applied to 21 programs myself, with a very top-heavy list that had no geographic basis. Things have gotten much more competitive since then, but I don't think blindly increasing volume without thoughtfulness is the way to approach the process.
For discussion's sake, here is a list of 21 programs. It's the same number I applied to, but a different set of programs. They all 1) have a track record that would not rule out fellowship, 2) are located in or near areas that suit OP's husband's needs, and 3) would likely yield a decent return of interview invites:
Massachusetts: BU, UMass, Tufts, Tufts Baystate
NYC: Mount Sinai, Cornell, Montefiore (Einstein), SUNY Downstate
Philly: HUP (they'll like the Step 2 increase), Pennsylvania Hospital, Drexel, Jefferson, Temple
Chicago: UIC, Rush, Loyola, Illinois Masonic (The step 1 score gets screened at Northwestern and U of C)
DC/Baltimore: UMD, Georgetown, GW, Washington Hospital Center
I can't in good conscience say another 29 programs would be necessary on top of that list. Maybe another 10. Each of those metro areas has other programs that OP could add to increase her chances of ending up in that location- though some would be reaches, and some would lack the academic/subspecialty aspect. Or she could add other locations to cast a wider geographic net- ie, west of the Mississippi, or major metro areas that don't have multiple programs (like Miami). Lots of options. While ERAS is certainly not the time to be cheap, I don't advise just throwing your money at it. You'll need it for flights and hotels later.