I'm not applying primarily IM but I thought I'd post here to help people strategize in the future. I am mostly applying community-based, university-affiliated IM for backups... since I'm not double dipping where I'm applying rads, and most university programs have rads.
I applied to seven IM programs total, carefully targeted. Three got a generic unedited IM statement, while the other four got a version of that statement where I replaced one paragraph with why specifically I liked the area and their program in particular, and sprinkled their name in in a couple other places. One site was my third year core site and another didn't take signals, so I got to signal all five of the other ones, which was nice.
I have a 5/7 yield so far. 4/5 programs I signaled have extended an interview, and 4/4 places I wrote an individualized personal statement for have invited me. The places that have not interviewed me have the mix of generic statement + signal and generic statement + no signal, and what feels quite natural is they're the places where I was just hunting for a couple more programs to apply to. I didn't think I had a good connection with them that I could explain in the first place, which is why they didn't get individual statements.
So I guess my advice if anyone is bothering to read is that no matter what your primary choice is, whether it's academic IM or something else, having some carefully targeted lower tier IM programs in your back pocket, that you made the effort to show a connection to and even wrote an individual personal statement for, goes a long way towards giving you peace of mind. I feel 100% confident that if my main plans fall through, I will still match one of these locations if I don't screw up the interviews because I am very much an above average candidate for them with a strong connection to their areas.