I have used 120dpi files at 120 lpi, it works! I had a very interesting conversation with a repro house in London about 5 years ago. I was always of the mind that 300dpi@100% with high lpi's was the only way. He showed me file outputs from much lower settings. Ok there is a difference but, it's easy to set the bar so high that nobody notices and this is the case for printing. I know it's a shame and destroys the quality that printers insist on. But ask Joe Public, they won't notice lower resolution (until you start seeing jpg artefacts). Or Joe Public just doesn't care. The only exception is small point sizes. That is a valid question and one I'm happy to concede to. But I still reckon 300dpi, 10pt or larger, artwork 100%, it will pass as being ok. Not fine Italian book printing, just fine.
Sure you can have huge dpi on the platesetters, Kodak, Heidelberg... Great on luxury coffee table books or car high-end car brochures, etc, done loads of that. I bet most image files you deal with are 300dpi (some are lower and you know it). The image setter is using interpolation to get those numbers. Isn't it?
I use Ai, the output settings is great for small printers, I agree. But you can't tell me most won't take a pdf? They want the work right?
Thanks for the non-offer too. I've done my time in pre-press and so did my father. No more! although I miss the smell of developer.
EDIT: although I say this and I truly believe it. I wouldn't dream of sending a photoshop file as a business card! And neither should the OP. I'm just enjoying the banter. It's nice to argue with someone who knows about printing