I agree. If you want a possible compromise solution, consider sending cards to ex-coworkers on birthdays or holidays. It's pretty easy if you use an online service to print and mail them and boy would that make an impression that you value their long term acquaintance. My aunt runs an engineering firm and does this with so many people, I remember driving with her to deliver birthday flowers and stuff.

That's all professional relationship building though, I truly don't think those people are ones she'd invite to a movie or over for dinner. Maintaining professional relationships does take constant low key attention though, if they only hear from you when you need something it's not a good look.