I find I can retain very good quality at 225DPI if I print on Photo Matte paper, but even at 225DPI you are only going to produce a print that is approx 5 x 4 inches. Upsampling effects quality and more so at lower DPI settings.
My advice would be yes, shoot again on film, or a higher res digital camera. Depending on the image you might like to try converting it to a vector. You won't get the same Photo quality, but the effect can sometimes be pleasing. Below is my reply, on another forum, to a post relating to this method and the image created. It doesn't work on all subject matter, but worth considering. Note, the vector program I used was Vector Eye. A google search will send you to a trial version that lets you save the results. You will need a vector app to convert from svg to a bitmap format.
I have a 2MP image of my parent's retriever Benson, shot with my Canon compact. With a little re-sampling and editing in PS, it prints a nice 8" x 6" at 245dpi. Because I wanted a larger 16" x 12" print of this image to gift to my parents, I decided to vectorize the image.
The original image was adjusted and down-sampled in PS, to increase sharpness, before converting to a vector. I can now have a 16" x 12" printed at 300dpi. I haven't uploaded a full 16" x 12" here because even at 72dpi it's a little too large. However, you can still see the image takes on a painterly look that is not displeasing close up. At the distance it is likely to be viewed when framed and hung on a wall, the photo-like quality becomes apparent.
At 16" x 12" at 300dpi the image is 16 mega pixels. No way could I have up-sampled the original 2 mega pixel image by this degree and got anything that would have been pleasing to the eye (at any distance). Even at 20" x 16" at 300dpi (28 mega pixels) a vector version looks pleasing when displayed at print size on my screen, and at 5 to 6 feet away looks very photo-like. Just goes to show what you can achieve by vectorizing a bitmap.
